I'm turning an APC 10x5 on my OS .40LA. It pushes the revs higher, so you have to be a bit more careful about lean runs, but the climb is quite good. I didn't try an 11inch prop in part because the 10" ones are cutting grass enough as it is.

As you can see, there are a lot of options. Don't be afraid to try something different. I do think a 9.5x5 is a bit small for that engine, but as you already know, it's not killing anything.

Also, different brand props at the same size can be very different, so sometimes changing brands in the same size will see a performance improvement.