I finished with 822 out of 1415 kills, or alternatively 634 live monsters, thus 781 dead (41 resurrections) so either 58% or 55%.
This was obviously not a blind run and indeed carefully planned and prepared.
I knew surviving the whole map was unfeasible. However, since non-finishers are ranked by killcount, I can get a good placement by racking up kills from the imp teleporters. I note several other players have tried this already; it's been dubbed the Thousand Imp strategy. But I believe it can be refined, to maximise its potential return. I require a large safe zone where the only active threats are the imp teleporters themselves, and an optimal amount of usable ammunition.
The obvious thing to do is to try to reach the keys. Each key gives a new weapon and access to large caches of ammunition. No need to go further unless you think it's worth going all the way to the next key, as going partway will simply expose you to further risk and deplete your health and ammunition reserves.
The Thousand Imp Strategy has a poor return using just the starting ammunition. I would like the blue key at least, for plasma and a few hundred cells plus a thousand more bullets. However, given the blue key, it turns out the red is not much more difficult to reach, and then you have three weapons, thousands of bullets, another few hundred cells, and a bonus hundred rockets. This is enough to finish with at least 700 kills, so is likely the optimal return. If playing "properly" I would need not only the yellow key but the fourth tower and the teleporter kill switch, and the map gets much harder after the red key, with multiple roaming archviles, sniper cyberdemons, and the like.
Then it's just a case of memorising all the traps and secrets along the way, and figuring out the safest way to clear each battle, then practising them over and over until confident of success.
I've played the wad before when it came out. I redownloaded it and proceeded to:
delete the horrible weapon sprites and sounds again immediately (I hope this counts as a "cosmetic mod", which I believe are allowed)
replay the whole thing in ITYTD, twice, to refresh memory
study most of the map in an editor to re-learn/memorise placement of secrets, triggers etc.
watch dist-3821.lmp (ancalagon's maxdemo) at 500% playback speed two or three times
watch everyone else's recordings as they were posted
work out how far I could expect to get with practice and degenerate safety play ("bourlasing")
make lots and lots of unrecorded practice runs (several dozen, over the course of the month)
finally make one and only one recording attempt as per rules, once I felt sufficiently prepared (realistically, never) or time was running out.
I don't believe I've broken the rules; charitably you could call this another "new breed of sensible ironman" run (as with BTSX where I stopped at a convenient point having passed the part that was ending most attempts, playing the whole thing was too long) but really, what I've done here probably takes gamesmanship to an extreme. But on the other hand, I don't think the wad pick itself was very reasonable either, so consider this a form of protest :)
The first area outside the blue key tower can be cleared with almost complete safety by hiding in the alcove with the partial invisibility secret teleporter at the back. You can also teleport out of here then back to base to restock/heal. Thus I think it's better to leave the blue armour for later. Watch for pain elementals getting into infights, though, you may have to dash out and regain their attention unless you want to deal with dozens of lost souls.
The most risky battle on route to the blue key is triggered by the third switch which lowers the large lift. At this point dozens of troopers plus revenants and an archvile begin to teleport. I found the best strategy here was not to try to run out and beat the rush, but to be partially invisible and lurk at the back. Eventually the cyberdemon will come into view and start helping you damage things from the back. I mow stuff down concentrating on revenants and the archvile until I hear a revenant wake up behind me, then dodge into the back corridor and open the teleporter to the berserk secret. I then jump around the teleporter network until everything is dead. I found this strategy slightly safer than rushing out, but it's the one place where I knew if I was going to lose the run, it would be here - usually the troopers hold up the revenants+archvile but sometimes they rush you or box you in, for example.
On this occasion only two things went wrong. Although I did get smacked for a big damage, it was before I picked up the berserk box, and I even managed to get the cheap telefrag in the secret. However, I courted disaster by firstly forgetting to get the blue armour before pressing the switch (the chances of an accidental archvile blast are quite high) and worse by not sufficiently carefully luring the cyberdemon out of harm's way before going up the lift. After I had the blue key I realised to my horror I would have to jump down the lift shaft with it at the bottom. Although I had full blue armour I could still have easily died to a couple of rockets at close range. Somehow though it astonishingly chose not to attack as I fell past. I then lure it towards the base entrance, into a spot where it can neither dodge much, nor hit me with rockets because the low wall of the "mouth" blocks it, safer than fighting in the open. This must really upset its brother the mouth guardian who can do nothing but watch :)
Onto the red key. Clearing the area outside its tower is easier, having the more powerful plasma gun, space to retreat to, and a lot of cover. Plus many of the monsters are fixed in place or can be dealt with one at a time. Overall it is much less chaotic. I then go behind the chaingunner gantry to another health cache and home base extension. I open the armour secret, but don't use the teleporter - it's much safer to go round, and clear it from the other side. Sadly, you can't get a second cheap telefrag here, I've tried.
Then I open the way to the red key tower. I try to kill off a couple of the pain elementals quickly with plasma. If you're good at dodging fire coming from behind, you can leave the teleporting imps for a bit, the pain elementals and chaingunners are more dangerous. I don't kill the two revenants until later because they're likely to get resurrected, I just use cover to dodge their missiles.
Now the red key's version of the nasty trap at the bottom of the blue key lift. However the sequel is nowhere near as risky. There's even a baron telefrag for free! I fill the air in front of me with plasma, and run as fast as possible back to cover outside. Unlike with the blue key tower, the only things that can follow you out are three chaingunners because there is a very convenient monster blocking line in the entrance. On the other hand I found it safer to clear the monsters inside myself instead of trying to get a monster fight going. The cyberdemon is an easy kill as it can't move, but do remember there is an archvile hiding behind it.
Finally I am instantly lifted to the top of the red key tower, into an ambush. You are rather exposed here so it's good to have as much health and armour as possible. Stay in the corner to your right and plasma everything in front of you quickly, then run into the corner at the start of the passage behind and kill the troopers and pain elemental. Basically use as much cover as possible and know how you're going to move in advance. Finally with the red key, I symbolically kiss its switch but don't press it, and return to the imp teleporters.
For getting the rocket launcher and a bunch of extra ammo, this is the one place where a partial invisibility is strongly advisable. Where you use the other two is a matter of taste, but here you will be instantly surrounded on all sides by hitscanners and it's so late in the run you really wouldn't want to lose it here. Blast your way out in the initial confusion.
All of this takes just under half an hour. I then spend a further fifteen minutes emptying the imp teleporter. Monster vertical aim is rather inaccurate - there are several places to make your stand where fireballs pass hilariously close to the top of your head without actual contact. Actually fully emptying the teleporter was unusual, I had only managed it once during practice and wasn't expecting it.
Eventually with no more targets I returned to the start of the map and ended the recording. I thought about sacrificing myself to the mouth guardian, but why give it the satisfaction :)