It's really hard finding definite informations about my questions. The R9 290X can be had for 299€, though a waterblock is slightly more expensive for it then for the GTX 970. The power target on the later card though is not really high enough to get good overclocks on the reference PCB if you want to watercool, so overclocked under water I'm still not sure which one is the better card
1. Even if you watercool a 290/290X, max overclocked, it won't really beat an air-cooled 1.5Ghz 970.
2. There is little point in watercooling a 970/980 since they barely have any voltage control and air-cooled MSI Gaming / Gigabyte G1 already run cool and quiet at 1.5Ghz overclocks, while MSI Gaming shuts the fans off up to 65C (idle/2D desktop work).
3. If you want to watercool a card that has real voltage control, then try to get an EVGA Classified 780Ti. At 1.3-1.4Ghz, it'll outperform the 970/290X handily at 2560x1600 or lower, while costing less than the 980.
980 at 1.48Ghz
At only 1.155 Ghz Boost, the 780Ti is kicking ass. With
1.35V voltage control , if you get 1.3Ghz+ on the 780Ti, it will be fast.
Otherwise, pick up used after-market R9 290s or 970s as 6 to 8-months stopgap cards until 390X/GM200. Then sell those and get 390Xs/GM200s and
then buy waterblocks.