Well, here's what I think as regards the larger clearances and power: Yes, smaller clearances give quieter running and (marginally) more power.... up to a point. My Flash has S-R pistons in it and I used to set it at .008 and .010. Unfortunately, when pushed hard (full throttle up a long hill, trying to hang with a T160 and an 850 Commando or extended runs at the Ton), the exhaust clearances closed up. Now, while it's entertaining to your mates to see 3 ft. flames shoot out yer tailpipe (picture the aftermath of of two Chuychangas with extra green chile sauce from Chuys, Mike) it doesn't do much for the go and I imagine the long-term consequences are also undesirable. Now, I haven't pushed her quite that hard since I opened up the exhaust clearance, but I'm guessing this is what they're referring to.