Dude, I think that a decent air cooler would be enough. If you got a good one, with the Antec 900 you could run the whole thing with a low RPM, keeping it quiet, yet cool.
yeah water cooling is only necessary if you really need 300 more mhz. but seriously you would never notice the difference outside of benchmarks anyways, and thats 100 euro's you dont have to spend.
LOL! Do you really want to go water on it? You'd have to buy a new case and then all the other WC'ing parts. I really doubt you'd be able to get a much higher OC with it too