As others have said, there's no way to know. There are variables in how different processors will oc - your QX6700 may overclock differently than mine. And your ambient temps will be a big factor on your water temp. Are you running this in an 80 degree F room or a 70 degree room? What's your goal for processor temp? Is your processor overclocked now? What temps are you getting?
If it helps, I'm currently running my QX6700 at 3.45GHz on air. This is with an excellent heat pipe with a ton of air moving across it. It stays at about 66-68 degrees when fully loaded. I'm moving to water cooling this week to try and get more speed and keep my temps below 70. I'm hoping to get to 3.8Ghz and have a much quieter system.