I am running a Q6600 @ 3.6 and a 5870 @ 930/1275, MY 3D Mark Vantage scores are as follows:
CPU Score: 12549
GPU Score: 18354
Total Score: P16452
On top of that, i have seen no difference with this video card in an i5 750 @ 3.33 rig at all, so, to answer your question, no, there will be no bottleneck. Maybe an i5 750 or i7 920 will utilize the 5870 a little more efficiently, but in no way shape or form is there a bottleneck.
I also noticed a HUGE difference between my E8400 @ 4.0 & Q6600 @ 3.6... the Q6600 @ 3.6 absolutely smokes it!
Hands down, the Q6600/6700/QX6800 series CPU's might be the champion of ALL intel CPU's ever made, at least in my experience...