J Hallock,
Actually, stability in the air comes from other things than the number of blades on the prop. You really are heading in a good direction, however, when you're thinking about experimenting with props. They sometimes do make a great deal of difference, and it's often from just changing brands, while keeping the same diameter/pitch.

The other day, one of the beginners at the field was telling everyone how much better his trainer was flying with the new prop. Turns out the new one was same brand, diameter, and pitch. When I looked at the old one, it still had the warning sticker (only slightly surface worn) stuck pretty far out one blade. I put it on my field balancer and that side almost broke when it hit the work bench. It's amazing his trainer was still in one piece. I'm guessing the reason his trainer was flying better was because the engine was running smoother, the fuel wasn't getting SHAKEN like crazy, and the new prop was biting the air along a straigher path (not to mention his receiver not being beaten to death or the gear trains in his servos seeing less abuse). With props, lots of things can change how the model "feels".

Most .40s will turn an 11x5 pretty much like they'll turn a 10x6. Trying them both would be worth the test, real easy to do, and wouldn't crowd the envelope for the engine one bit. And would be a really good thing to do along with testing the 3-blade, if you find a 3-blade that fits into the system. Hey, trying different props is actually a lot of fun.

BTW, every prop change should be followed by a basic readjustment of your needle setting. First thing to do ALWAYS with a new prop is to turn the needle out until the sucker clearly goes rich. Count the clicks out so you won't get lost. Then adjust back down from there. Going out to rich gives you a safe and dependable starting point.