I have a OS.91 FX with a pitts style muffler in a Minnow. The .91 lists 2,000-16,000 rpm and several prop/rpm stats at the towerhobbies web site. A couple examples are 13x10 @ 9500 rpm or 14x10 @ 8400 rpm or 14x8 @ 9500 rpm. I am wanting as much speed as I can get so which prop best suits my needs? or should I drop down to a something like a 12x12 or 12x10 to get towards the high end of the .91 rpm range? & would a tuned pipe help as well?