My friend got a 7900GT and it sounds pretty quiet to me. The X1900XT/X IMO isn't that loud. I'm waiting till HIS releases their X1900XT/X with the IceQ3 HSF. From the previous IceQ (I and II) they are the best ATI HSF, and it runs cooler and quiter then the 7900 GTX stock HSF.
I don't want water cooling even if I had the money to buy it. Noise isn't a big deal to me, especially since I use headphones and don't hear the computers most of the time. Even at a LAN party I couldn't hear a X1900XT very loud either (it was a private 8 person LAN so there wasn't that much noise.