I would just add that anyone contemplating this mod or anyone coming across this thread in the future, there were a lot of unanticipated issues that cropped up along the way--all solvable, but it would help to contact someone who has been through this before getting started with the project. There are no Vans "plans" for this, so it pays to do the research prior to beginning. Having done this, John and his brother Dave have acquired a wealth of experience, so I would contact them for an overview if you're thinking about doing it. In John's case he was looking for the nicest possible RV-7 out there. The one he found happened to be a 7A, and I commend him for getting the nicest airplane available and then making it the way he wanted it! I think he'd be the first to tell you, however, that it was a lot more work than he had anticipated! But it was well worth it in my opinion!
I can't answer the question about the speed increase, but John did fly it alongside my RV-6 after it was done for a full-power comparison and they were pretty even, basically same engine and prop. And my -6 is pretty fast!