I really don't think watercooling is even necessary other than maybe for subjective aesthetic purposes or just outright preference for the GTX 9xx's, that is for the people who aren't going to unlock their bios and increase voltage thresholds beyond stock. Even then, I don't think a + .03.-05. mv to either increase the core clock or fully stabilize the core is going to generate more heat than what both reference and custom air cooling can easily handle with cards that weren't a bad luck in the draw (i.e. poor TIM application, alignment of the heatsink, etc).
Whatever you get, 4gb of vram will provide more longevity than 3 gb's. With 970's for SLI and the pretty much non-existent price gap between the 290's and the 970's with all the...