Get a good heatsink, and OC it until it gets very close to 60C or you get to a speed you are comfortable with. Im not sure if its possible to OC it high enough to not bottleneck 3 GTX285s fairly significantly, the highest you can expect to be able to OC on air is about 4 GHz
The V8 isn't the best. It is hard to install (I know, own one myself). As for cooling, it isn't bad, but currently my system isn't overclocked. It is also expensive. Other coolers give you better bang for the buck. If you do decide to get that cooler, you could probably overclock to 4 ghz as long as your cpu is DO stepping. CO may not fair as well, but it's possible.
You really can't figure out how much your going to overclock before you do it. As for coolers, I really liked my domino a.l.c. (water cooler) and it was only $70. You can check it out on newegg or buy.com.