For the MVVS GAS question, A tuned Exhaust will enhance your performance. Go for it. For everyone else, each has hit upon very valid points and we all learn from them. The biggest point to consider is that a tuned pipe can be adjusted for different applications. Typically this is done by the experts. With joe average, A MACS pipe is used for max speed on 2 stroke glow motors. Other pipes are available for other apps. On gas motors the Tuned exhaust is to make the motor responsive at all power settings with a benefit of a slight rpm increase at WOT.

For the original question that started this thread. MACS makes a pre-tuned pipe/header package for your motor. Try a 10x7 or 10x8 APC with it and go from there.