One school of thought is that you should peak at the 1,000 foot mark which by then most of the acceleration has reduced your ET and you are already at a higher MPH for the last 320 feet...

This assumes the engine can handle the rpm and is not nosing over...

My motor made peak HP at 7,200 rpm and I cross the stripe at 8,000 - 8,100 rpm. I think it ET's decent...

Best way to find out is to test it, so let us know how the 4.56's affected the ET and MPH once you cahnge.

Cheers,

Arnie