I've had a 30 to 50% drop in FR as well... Went from 35 - 45 and fairly stable to a base 23 to 25 which drops like a rock to the 8 to 10 range in smoke or multiple plane environments...
System:
P3 800
392 SDRAM
nVIDIA GeForce2 64Meg MX/MX400, by VisionTek
SBLive 5.1 XGamer
DX 8.1
have reloaded sound drivers, video drivers, tried new and older versions. Playing with different memory mangers now...
--> One note, am using a HBlair hand-me-down MOboard and processor which he was getting much higher frames with on a 32Meg card and less RAM. <--
I also have a Win2K Pro configuration using the same MO & Processor combo which produces poorer overall FRs and gives me a nasty little intermittent flash at the bottom of the screen in AH only. Have tried other online games without the problem. & BTW newer nVIDIA drivers, (from nVIDIA, VisionTek, and MS Update) and WIN2K do not work with AH on my FE (get a green screen and clipbaord rings when loaded but it doesn't lock up the system, have reset my video7.cfg file to every setting with no joy). I have tried drivers from nVIDIA, VisionTek, and Windows Updates... Old, new, and yesterdays newest update @ nVIDIA. The only ones that work for Win2K are the originals that came with my card - all however seem to work normally with Win98SE @ a reduced FR.
Reading the comments posted in other areas, I am inclined to believe that the nVIDIA hardware/software and AH might have a conflict depending on the nVIDIA board manufacturer. Seems to be a recuring theme. I have also researched VisionTek's track record. They seem to be a reputable producer of quality products. I either have an isolated problem with my card, or my system might have other issues affecting my video and drivers... Can you say "format C:"? Before I do that, I'll wait for my query to their customer support and HTCs before I get that drastic... maybe.
Any suggestions for me to try would be greatly appreciated.