11x4 could still be under-propped, you really need to check it with a tach. If you want to stay with an 11" prop, 5" pitch would probably be the lower limit. Unless you're looking for more speed, I wouldn't go with the 10x7. The pitch of the prop will usually make a difference in the landing speed. In most cases, the larger the diameter of the prop, the slower you can get the engine to idle due to the flywheel effect. A smaller diameter prop with more pitch is gonna fly the plane faster at any given throttle setting, including idle.