I have the exact same problem with my box:
AMD K6-2 500 MHz
128 MB memory
Voodoo 3 3000 AGP (STB) 16MB
ST320423A and ST340014A
Amigamerlin 2.9 is installed, also I installed the nfs4xp2eng patch:
-Windows XP support
-best 3d Setup - no bugs
-fixed 1mb free space problem
I've also installed the official 4.50 patch
Also I've tried to run the game without any patching - it's aaalways choppy, especially at the beginning of a race when all the opponents are in front of me.
It doesn't make a big difference if i try it in 1024x768 or 800x600, the biggest difference is seen if i reduce effects and details to the absolute minimum.
what the heck, i remember i played that game on my P1 166mhz with voodoo 3 pci 16mb smoothly at 1024x768...
also: if sim tower runs in fast mode, the mouse is extremely laggy and the sound gets ugly like if the cpu can't keep up. but sim tower is a brutally old game...?
nfs 3 and nfs 2 se run perfectly, also future cop LAPD or GTA (dos mode). n.i.c.e 2 runs also very good.
Midtown Madness 2 is very slow, even at 800x600 and low detail settings.
can you give me an advice where i can start measuring and troubleshooting? I could really use some benchmark comparison values too, very hard to find that these days.