I think the deal is this; the 440-1 heads will show better flow numbers and increased power when you go with a large bore (4.5), not hard to understand. The 572-13 came with a valve as big as you can reasonably put in the 440-1 casting, then there is the optional 2.35 intake, but you still are saddled with the same casting, valve length, etc you have with the 440-1. Once you realize the power potential of any wedge head is the length of the valve stem, (limits port shape) you can understand why this head will have a performance limit higher but still close to the 440-1 if both styles are taken to their limit. At that point, if you want more power, look at the valve lengths of the B-1 heads, and the brewers, They dwarf the 440-1/572 deal, at least the brewer heads do.