If you are going to be water cooling, the only option is the 290/x...ESPECIALLY in multi-card setups. Clearly power/temperature/noise is no issue to you if you have 3x 480's.
Nothing performs faster in multi-card setups at any price, and yet the 290/x cards are relatively cheap. Absolutely go that way if you are looking to upgrade now, the 290 is the best value...but being just released the 290x are going to be the best harvest chips...and may offer much more performance under water (the stock cooler holds them back hard).
The only other thing to consider, is to wait for third party cards with better power delivery/PCB so you can overclock more/better. The current release is OEM/stock only and the default setup (w/ 5+1 phase) isn't the best.
Anybody recommending a GTX Titan is a fool. The 290/x performs on par for HALF the price, thanks to the advancement of technology (and Nvidia's horrific pricing).
The 780ti is an O.K. card if you only want ONE. In multi-card setups it has less VRAM and less performance than the 290/x cards and it costs much more.