A You're on the right track. All things being equal, gas flows more efficiently through a straight section of pipe, but any good exhaust system needs to produce power throughout the rev range, not just on top. According to AMA Technical Director and former Team Honda crew chief Al Ludington, "On a bike with stock head pipes, the diameter of the exhaust tubing is probably way bigger than it really needs to be. The bends don't offer any kind of meaningful restriction. If you were to dyno the straight pipe and the S-pipe back to back, I'd be really surprised if there was a power difference. Usually the S-pipe will package a little better and offer better cornering clearance and access to things like the oil filter and drain plug. Ask yourself how often you use full power when you ride." If the answer is not that often, a slip-on with an S-bend will work fine.