Most reliable way of establishing par times

The par times I set for my SP maps are not the most reliable, for a number of reasons.

+ I am a terrible player, let alone speedrunner.
+ I know the maps better than anyone else.
+ I usually play on HMP and use ZDoom. (I think for many of my Jenesis Pt. 2 times I actually played on UV.)
+ I save in my playthroughs because whenever I try to go past the monsters I place, EVERY single one of them somehow manages to hit me. I swear that the hitscanners have aimbots whenever I enter a room.

All these factors, while unrelated to each other, do contribute to what seems to me to be a terribly inefficient means of establishing par times.

Is there a technique to this that I should be aware of?

I set all the par times for DOOM 1 by starting the level, running to the exit as fast as possible, rounding off the resulting time, then adding 30 seconds for padding. I actually got those levels done faster than the par times.

http://5years.doomworld.com/interviews/johnromero/page3.shtml

Yeah, that's basically my strategy, but it's so infuriating the number of times I die just by killing as few monsters as possible, especially on UV.

Also I do add a few extra seconds - about 10 or so, though.

Get about 10 average players to play the map, have them play with identical settings, then have them record their times. Average all those times together and that's your par time.

I think Romero did his runs for this purpose on HMP. I don't have a source for that. There might be one, but it might just be general supposition.

If you find that on Zdoom you get shot more as you run past enemies, it might not be just your imagination. The change in blockmap handling dating back to Zdoom 2.0.51 will tend to have that effect. Possible solutions: use a different port, or set the compatibility option "use Doom code for hotscan checks" to "yes". (I think that's the relevant option; or just use "Doom (strict)".)

I personally just leg it through without making any real cock-ups once on UV using ZDoom. If I die or get stupidly stuck, I just try again. Usually works quite well. However, if the map is huge or stupidly difficult I'll go for a UV Max run, with saves to aid in my quest. Always helps to mention what your deciding method for par times was in the text file too, I think.