Juice,

The 10x8 size will give you as much load as an 11x6. If you use the Master Airscrew prop, it will not be as heavy as an APC and your engine will be turning approximately 11.8K.

If you change to the Hobbico .46 muffler (I am told it is the exact same as the Tower muffler, at a little less cost.), you will be getting 12.3K.

A gain of 500 RPM is 13% in horsepower output, which is a difference you can really feel.

A 10x8 at 12.3K will give you more calculated speed than a 10x6 at 14.5K.

At $13, it is much less expensive than any "real" pipe.