My 408 is all done at 6200rpm, and it is actually more throttle responsive with the 1000cfm quickfuel carb than it was with the proform 750! Must have been the tune, but I also picked up 2 tenths with the switch to the bigger carb. (M1 single plan with a one inch Wilson spacer) Also, the increase was observed on pump gas originally, and now still works great with the E85.

Pump Gas Small Blocks Rock! 11.53 @ 116mph E85 408 at 8500 ft da, 3605 pound truck, 3.91s, street driven