first thing you should do is replace the heatsinks on your card. get 2 blorbs or something and put them on the cip. also, put 2 heatsinks(dont have to have fans) on the back of the card where the chips are on the adjacent side. if u want u can put it on the ram too, but they dont get too hot. after u have that utility in 3dfx tools, over lcock it by small intervals. start with 175 and go up by 2s from there. if it doesnt boot up at one of them, or is unstable, go back down. to test it, get 3dmark or quake and loop the tests or demos. make it run for like an hour, and if that works, u should be fine.
overclocking the v5 doesnt really help that much, but it doesn increase fillrate. if u get up to 183 then the fillrate is 733 as oppose to the 667 which is default. that was the setting they originally had for the v5 but they had to push it back cause they wwanted to get the card on the market as soon as possible.