Can you just try the geforce to see if it makes the difference?

Which mainboard you are running? With VIA (MVP3 or MVP4) or Ali ALADDiN V (which revision ?)

With 256 MB ram, you don't have write-back cache strategy (except you use K6-2+ or K6-3(+) with on cpu L2 cache). see here: http://www.amd-k6.com/cacheable-ram-on-socket-7-platforms/

I have with my K6-2 500Mhz, VIA MVP3 board, with a Riva 128 PCI and a Riva TNT2 AGP, 64MB PC-100 ram (with write-back strategy) , 3Dmark 99 (default setting 800x600) :

with Riva128: 922 (3Dmarks) , 5878 (CPU 3dmarks)
with RivaTNT2: 2588 (3Dmarks) , 5971 (CPU 3dmarks)

For example, look also this thread:
Voodoo 3 3000 AGP under performing?

The motherboard is an ASUS P5S-VM, however it's one of the HP ones, I don't think I have all the BIOS options available to me. It looks like the chipset is SiS530/5595.

What prompted my initial post, was I'd just installed System Shock 2, which looking at the recommended specs should be easily playable on this PC.

https://www.mobygames.com/game/system-shock-2/techinfo

at lowest settings, I'd estimate I'm seeing about 10fps @ 640x480. Looking that the other threads you posted, my 3dMarks seem pretty standard for this build, but most gaming seems very sluggish.
Thanks,
J

Ok,
according to wiki the SiS 530 can cache up to 256MB ram so that is not the problem...

The member Skyscraper has benched this chipset against the other availables:
"Super 7" SiS 530 chipset.

Here i have a chart of a review to system shock 2.
With a P2 -333 it should be fine...

That chart is quite telling. Perhaps I'm expecting too much, it might be time to replace with a Pentium 2 or Pentium 3 system, maybe P3 @ 1000Mhz.

Have installed shortly system shock 2 to these my example PC's:

• K6-2 500, clocked @400MHz, VIA MVP3 chipset (512kb L2 cache), 64Mb RAM PC100, Riva TNT2 32Mb SD-RAM.

Example Screenshots.

• Athlon 1200, clocked @550MHz, VIA KT133 chipset, 512Mb RAM PC133 (clocked: 100MHz), Riva TNT2 Pro 32Mb SD-RAM.

Example Screenshots.

Melbar, thanks a lot for spending this time on this, this is so helpful. It looks like moving from a 400Mhz CPU to 550Mhz is netting almost twice the framerate. It's easy to forget the pace of change between about 1995 and 2005 in terms of processor speed and what they could achieve. A new CPU one year may have struggled on a game released even 12 or 18 months later. Your post has reminded me that I'm trying to play a 1999 released game (possible a quite demanding one at the time), on a CPU from early 1998. This seems insignificant in retrospect, but a CPU from 2000 or 2001 will likely run this game far more smoothly.
Again, thanks for the time and effort you put into this,
J