Go to http://www.geocities.com/siliconvalley/campus/5009/javamazeintro.html
I remember Doom was quite acceptable on a 486-33MHz. Even with the Java slowdown, a 1600 MHz Pentium 4 running Java should be able to matchup with that, especially with Just-In-Time compilation.
I'm actually thinking of starting up a project to do a Java port of Doom just to show that it can be done, and to sharpen my Java skills. I am a programmer by profession, and though it would be complex, a Java Doom port would be much more interesting than the programming I do for my job.