I might do that too until I have some help installing my rear ebrake. I've seen a guy in Austin running the 6pot pro-series Brembos ($3k ones) just on the front of his GT with oem 19 wheels, it seams like he ran without any problems. I think running stock would be fine, but for me am planning on doing the rears later, but I don't think I would like the look for the long run.
I will soon be running 6 pot CTS-V fronts with stock rears....... I currently have the 4 pot Brembro's up front. I don't have a problem with it. Sure the 4 pots would look great on the rear, but then I wouldn't be able to fit my 17" GTO rims with the Mickey Thompsons.....
How about stock rotors and stuff in the back but slotted and/or crossdrilled rotors up front? I don't need rear brakes yet, I will need fronts soon, hence me either getting good rotors/pads up front or just upgrading to the CTS-V stuff.
I know the newer Mercedes come that way(drilled up front, non in the back), wasn't sure how it'd look on the G8