The Voodoo1 would be the bottleneck, you are using a Voodoo3. Actually I wonder which tweaked settings hwupgrade.it used, usually 30fps is glQuake with Voodoo1, Q2 should be slower.

OK here are some benchmarks on the 233MHz, I'll do the 250MHz latter.
Doom: 99fps with l2 cache, 89fps without l2 cache, 15,4fps only l2 cache, 6,2fps without l1 and l2 cache
pong:1813fps with l2 cache, 1775fps without l2 cache, 305fps only l2 cache, 121fps without l1 and l2 cache

MDK2:15fps
3DMark99 score: 1067 min, 1298 max
Quake 2 demo1:38,1 with sound, 41,1 without

EDIT :
Processor at 2*100
3DMark99 score:1254
Quake 2 demo1:38 with sound, 41,4 without (the clock is 33MHz lower but the performance was almost the same, that's interesting)

EDI2 :
Processor at 2.5*100
3DMark99 score: 1424
Quake 2 demo1:43,8 with sound, 48,1 without

EDIT3: OK I didn't saw any difference in most games, but with sound card disabled I really saw a difference, I think maybe my problem is the sound card, and then I think, is it possible to mix sound cards without performance drop? like use the isa sound card only for dos and the pci sound card only for windows

EDIT4: I found a jumper on manual that said if I set it to agp it would use agp clock for DRAM, if I set it to cpu it would use it the cpu clock to DRAM.
I'm not shure if it's l2 cache or sdram that he's talking about, but I changed it to CPU and I got some extra horse power.

Processor at 2.5*100 , 100MHz DRAM
3DMark99 score: 1542
Quake 2 demo1:45.8 with sound, 50.1 without sound (13.2 without sound in software with 640x480 res)

I think I ended up into a conclusion, the isa sound card doesn't actually hit the performance by being an isa sound card, and yes by lacking hardware aceleration (there was some messages about directsound and directsound3d but I think it's a lie), and since there's no sound aceleration, the hard work end to cpu, that waste some extra power for processing sounds.
Maybe with a real sound card with real hardware aceleration I could have zero cpu inpact when playing sounds.

Other interesting fact, the pentium mmx233 is more powerfull then he overclocked to 250MHz when you disable L2 and L1 cache, but if any of those are activated, then the pentium 250 will be faster.

Also I noted just a big upgrade over quake 2, maybe it's because it does just simple sound processing (38,2fps -> 45,8fps)
MDK must have a more complex sound processing so there wasn't any changes at all (15 -> 18,8fps)
Star wars racer too, but now it's not going below 20fps (max 30fps min 16fps -> max 40fps min 22fps)

Resuming this history, games that was running well got a big increase, and games that wasn't reaching 30fps all the time didn't got a boost, but max 3fps increase