Go for the 6700 OEM and get THIS CPU cooler, should keep it fairly cool and is better than the stock cooler by far.

6700 = 266 x 10 = 2.66Ghz and the 6600 is 266 x 9 = 2.4Ghz. I have the 6700 and it's bloody fast, even at stock!

In terms of Motherboard, either the Asus P5Q or Asus P5Q Pro will support C2Q, and hace PCI-E 2.0 and a lot of SATA ports for your storage needs.

The P5Q is a good base, but if you want to get away from the crappy 24-Pin location or have scope to move to CrossFireX in the future, go with the Pro version. (Google and find out the Qualified Vendors List for RAM on the mobo before you buy though, it can cause some problems down the line.)