The big difference in TNT2 Ultra boards will be which runs quickest, most stable, and has the best support. The Diamond Viper v770 Ultras drivers have one unique aspect amongst most others, and that is the ability to adjust the core speed (not memory) with a booster bar in the drivers. In increments of 5MHz, there are 5 different levels to boost the core of the TNT2 Ultra. Ranging from 150MHz (default) to 175MHz, the boost levels are configured per game you run. This is highly useful since we've seen that some games run great at 170MHz, yet others can crash at that speed. Since the core clock speeds can be changed on the fly in Windows, this makes changing it per game a very easy and viable solution. The memory speed stays at 183MHz the entire time. You can of course download third party utilities to adjust this. We found that overall 175MHz was the best speed for the Viper v770 Ultra. At 175MHz most games were stable, and for those that weren't, we just used InControl to keep them at 170MHz. This again proves Diamond's super driver support in keeping the gamers happy. We couldn't do too much to overclock the ram, as the Elite MT 5.5ns ram was pretty much at its maximum.
I must admit that I've never been a great fan of overclocking to high limits as it tends to take up too much time in figuring out which specific component can do what. The Viper v770 Ultra is overclockable, but not as much as other TNT2 Ultras we've played with so far. The Hercules is said to be great for overclocking (although we can not verify this), but then again, you'll have to put up with Hercules drivers and support, and that almost justifies not buying their video card. Keep it safe and stick with Diamond.