FYI. I got my answer. Both acceleration and top end are down slightly with the new 502. In a two day trip on the ol' Miss, the 430HP 502 is MUCH MORE THRISTY than the ol' 496HO. sorry no meaningfully mileage numbers but the the 502 had to stop for fuel half way back up the river on a trip that has always was done in less that an 85 gallon tank of fuel.

I think I'll keep the 496.