First off, note he said quartersawn. That means he started with a board, and edge grain at that. Rawhide is an incredibly sensible choice for backing and the weight of thin rawhide backing adds only a few grams of weight out on the tips and the difference in speed from the arrows would be maybe a loss of 1-2 fps, which is still going to be significantly faster than the most efficiently designed and executed broken bow.
Secondly, I see nothing concerning about the tiller, nothing that would keep me up at night, much less cause me to break out a micrometer to try to quantify.
As for worshipping the Gods of Speed, unless you are seriously considering a trip to the Bonneville Salt Flats for the International Flight Shoot, it's really just academic. EVERYTHING in making bows and arrows is a long series of tradeoffs. High efficiency/high-speed bows are generally short-lived and break at the worst possible time, as per Murphy and his law. I'll trade off that speed for longer limbed bows that seem to be more accurate and sweeter shooting.
Now settle on a design and start making woodchips, and be sure to post pics of progress as you go. We are all about seeing what others are making!
