I just played a mostly successful game... as in I got to Kornel, but then died... :P I must say this version of the game is considerably harder than the one I played in my videos! :|
Anyway, I seem to have misunderstood how the boss system works. It seems that you face KK every time you complete level 5. I thought that if you haven't killed the Cyberdemon or Spider Mastermind by the time you complete Arena level 5, you could keep the game going longer. Like you would face Cybie after level 5, then the MM after some later level, and then finally KK after some other later level. Alternatively, I thought, at the very least, you needed to have Conqueror for KK to appear. This run disproves both of these; after level 5, I had no choice but move on to the boss stage and face KK.
The special level before level 3 was Gotcha! (the level with Cybie and MM) and I deliberately skipped it, running right past both of them, so I wouldn't get credit for killing them, thinking that this would help the game go on longer and get me a higher score. (It shows in the picture below that that's the one level I didn't complete)
I guess this means that my top score is truly unbeatable! :D (Since I got it in the previous version with more levels; oops!)
EDIT: Oh yeah, what if I actually include those screenshots? :P