RegHardware take a look at the Sapphire Blizzard X1900 XTX water-cooled graphics card:

The X1900 is - just - better than the 7900 GTX. However, if you play specific games you may well find that the reverse is true. The Blizzard removes the main concern we have about X1900, ie. the noise, but it can do nothing about the fact that we have a personal preference for Forceware drivers over Catalyst. We also prefer SLI to CrossFire as it's a more mature system and at present there are no plans to introduce a Blizzard X1900 XTX CrossFire master card so gamers will be stuck with a single graphics card unless they run a noisy air-cooled Master card alongside their Blizzard. Funnily enough, the price is the least of our concerns as there are plenty of premium graphics cards on sale for £499 - £60-80 more than the Blizzard is expected to cost.

Deciding whether you should buy a Radeon X1900 or a GeForce 7900 GTX is a tough decision, but on balance we would favour the Nvidia card because it's quieter and has better drivers. Blizzard changes that and means that we now vote for the X1900 provided you have no plans to run more than one graphics card inside your gaming PC.