BTW, it's just a Q6600. It's not a Core2Extreme. It's just a Core2Quad. It's not unlocked like an Extreme. And If he really wants to go quad, and price is no issue, I would recommend the Q6600.
With water, he should be able to get a decent OC with a few boards (eVGA 680i (A1 revision) comes to mind). eVGA is basically the only company to knock the kinks out of quad-core overclocking in their 680i chipset (A1 revision). The AR and TR revisions have the same problems that other boards have with quad-core overclocking, hitting the top around 370 FSB.
The X6800 will be able to clock a lot higher on water, but if he's going to do a lot of multi-threaded or multi-tasking with intensive programs, then the Q6600 is probably the way to go.