Charlie, thanks for bringing this up. It's a thread worth reading, and should be over here as well.
Neal's data is really fascinating. While nothing is perfect, it's some of best data we have on this issue, by a super consistant driver. His analysis is very interesting and spot on. HP means less for lap times than track position. 8/10's of a second doesn't seem like much, but 117 feet is 8 car lengths all in the straights , which is not the same thing as just driving 9/10ths. While chassis setup can make bigger differences in lap times than normal HP variations, there is an interesting aside to this. Given cars that are capable of equal lap times at a given track, the cars that does it through HP will be more competitive in a wheel to wheel racing situation than the one that does it through handling.
There's another difference between handling and HP. Setting up a car well for a given track (and appropriate to their driving style), is part of driver's skill set. HP variation relates solely to the car. This class is all about showing (and developing) all of a drivers skill set, and as little about the car itself as possible. This is the reason that 944 Spec allows more chassis adjustability, and less HP variability than most Spec classes.