RE: Team OMP Presents the Boxxer ARF!
With Spektrum/JR 821s in my tail, and the Saito 82, I have pretty good balance at 1.25 inches (forward) from the TE of the top wing. Really, 1 inch is about optimum, so your 645s in the tail will likely help out.
I also agree that 4 servos for the wing should be kept to Minis or even micros as Mike mentiones. 4 standards would be needless weight.