Mike,
Some interesting information did come from my inquiry. From reading different posts over the years in this forum i got the impression that racers that used carbon pipes were very strongly biased toward their use much like the racers who own Cooper pipes seem to be. This thread generated no replies from racers using SPP or Gadget pipes though. Although I currently own a vast assortment of different outboard pipes and different power heads and hulls, I’ve never taken the opportunity as you did back in 2005 to do back to back testing. Back when I got started racing tunnels in 2006 I started with a MAC power head on a K&B lower, with a Irwin muffled pipe pushing a TopSpeed 2. Shortly after the engine was broken in the hull was replaced with a XTR-21 Leecraft which I raced for two seasons. During the second season I changed to a Silver Bullet HP pipe with no noticeable change in performance. I had similar results during the same time period with my 45 tunnel. Axe Rossi River King/K&B lower/muffled Irwin, on a XT 460 Leecraft, then switched to a Silver Bullet pipe. Prop changes have shown me larger performance gains or losses and also some require the boat setup to be adjusted.