I have an OEM machine with a 32MB nVidia GeForce 256 graphics card. By downloading the tweak utility and the latest drivers, I have pushed it to 125/175 from 120/166.
Unreal Tournament now runs about 15-20 percent faster, so most of that is the driver...
The question is how far can I go with or w/o fan?
Which fan should I get... I'm thinking the Blorb?

Abe
Intel = "I caNT bELieve you."

Your Geforce256 doesn't have a fan? I've never heard of one without a fan. Or do you mean "w/o a fan" upgrade?

As to overclocking all cards are different but in general some brands overclock better than others. My OEM Visiontek Geforce256 SDR overclocked to 145 core/210 memory but would run for only an hour or so before having difficulty. I replaced the fan with a 486 fan and installed DRAM heatsinks. The card won't overclock much higher but seems to run all day at 145/210. (That's with the case open. Geforce256's generate a lot of heat). By the way I did get to go 150/215. It only ran long enough to run 3DMark 2000 before developing pixel errors. It did keep going but it looked terrible. I have heard of people overclocking as high as 158/225 (or close to this). I don't know which brand they were using.

normally leave my card at only 135/185 which allows me to run most 3D games smoothly.

The problem with pushing a video card too far is POOF! or maybe just damaged memory which will result in ugly output.