Alex,
I would prop the engine down a little. It sounds like the 11x7 is a little too "tall" which might mean that the engine is not able to get into it's power band. If you are looking for thrust, sacrificing speed, go to a 11x6, or if you want speed sacrificing thrust, try a 10x7. Either one of these props will unload the engine and allow it to rev a little higher, maybe giving you more of both.
Good luck,
Curtis