bobby,
I may have been a little snide in my comment, and I apologize for that, but it seemed that everyone was saying the prop wasn't enough load for the engine, and all your replies only said, I like the sound.

An 11 X 4 is better than a 10 X 4, but still a bit small for the engine. The 10 x 7 will give you a considerable increase in speed over the 11 x 4, and will properly load the engine, which in turn will likely result in better overall performance because the engine will be operating closer to peak torque.

An 11 x 5 MIGHT be the optimal all around prop for your engine, but as you said, you need to buy a few within the operating range, try them, and determine which best meets your flying style.
Dennis-