Have you tried the Neon 250 patch for high speed intel CPUs? IIRC troubles start above 800 MHz.

I've never experienced any issues with my Neon 250 as you're describing. I used the drivers available here on vogonsdrivers. It's a long time since I tested my card, so I can't remember which board(s).

Maybe Gona can give some help, he has a Neon 250 as well.

From rough recollection....

Oldest drivers - Most SGL compatiblity - Needs oldest neon vbios, Intel CPU max 600Mhz? PIII, PII or Xeon (Tanner)
2nd oldest drivers - Medium SGL compatiblity - Needs Intel CPU max 600Mhz? PIII, PII or Xeon (Tanner)
Newer drivers - Less or no SGL compatibility - You add specific patches for >= 1GHz CPU, any AMD CPU, DX compatability improvements

My experience
- black screens without newer drivers and the 1GHz patch on a Tualatin, 815e
- error on boot without newer drivers and AMD CPU patch, for a Thoroughbred, KM133
- 0 issues when using older drivers without patches on a Pentium Xeon 550 2MB (Tanner), 440GX even when overclocked

- you might want to force AGP 2X or even 1x on some systems

Useful thread:
Ultimate PowerVR SGL card/rig/games?

Edit: when I mention AMD patch, it could of been AMD CPU support needs the newer drivers.. something like that

Thanks for all the info guys, I’ll take another crack at this weekend. Sounds like I can just lower my CPU speed for some quick tests? Was running a Tualatin at 1400Mhz for most of my testing.

For some reason dropping a 1400 Tualatin down to 66Mhz FSB - @700MHz did not alleviate my issue on the 815e platform.
(Multiplier is locked)

Maybe it will work for you
If not switch to a PII/lower PIII + 440BX combo should def work

I got it running guys! Applied the 393 patch and started getting the black screen as mentioned. Went back into my bios and remembered I had changed the “Video Memory Cache Mode” when attempting to troubleshoot. I set this from USWC back to the default UC and viola! Booted into windows and ran GLQuake no problem, even at 1400Mhz. This was on the Asus p3b-f. Thanks for the help everyone!