You can overclock the card too high...
I got an Asus V6800 Deluxe in May and the card rocks. Since I don't want to rip the default heatsink/fan I just placed an 8cm case fan blowing on the card and I was ready to go. First I must say that not all unofficial drivers overclock as much. For directX 7 (3DMark2K) you should use dets 11.xx whereas for directX 8 (3DMark2K1) you should use 12.90 which are the fastest around.
Here are some results to show you that you can get even a 25% increase through overclocking. The card is clocked at 120 core 300 memory. I use Riva Tuner to overclock cause it permits me to go over 150 MHz core. So the max I got out of my card before the image quality became trash was 172MHz core and 372MHz memory. After this I get 3152 (2K1)with my PIII 1000@1027. When it is clocked at default it gives about 2500 3DMarks2k1.
Geforce256 DDR is a great card and I got it by chance. I was off to get a geforce2 MX and a TV tuner with the video in (I didn't need the tuner just the video in) and I found the deluxe card I got on sale for 175$ (prices in Greece are too high...the Asus 8200 Deluxe-geforce3 is 465$). The funny thing is that the Asus deluxe with the MX chip was about 40$ more expensive...I love my card..
crAss
PS. I was thinking of one more parameter to the overclocking of the geforce256 DDR...We assume that all cards are the same. We know that the memory modules differ but we say that all nvidia chips are the same. They aren't cause they are produced same way as CPUs. They have steppings and as the production goes on the chips that get out of the production line are even better as far as quality is concerned and thus they should overclock better. The card I have was manufactured on April 2001 and so for me there is a possibility that it overclocks better than the same card that was produced over a year ago...
System specs
CPU: PIII 1GHz@1027 FCPGA on a slocket
MB: Soyo 6BA+III (BX chipset, AGP 1.0) with the latest BIOS
RAM: 1 dimm 256MB-->133MHz CL3
HD: WD 40GB 7200 ATA100
VGA: ASUS V6800 DELUXE
Sound: Diamond Monster Sound MX300 (Vortex 2)
Modem: 56k rockwell chipset int winmodem
ISDN serial modem
DVDROM: Hitachi 2500 BX
CDRW: Plextor 8432T
5 fans, 3big and 2 small
300W atx power supply (specifically 160W +5V, +3.3V combined)
OS:Win98SE, DX 8.1