APC 9x7 - 9x8, it is not going to be much faster, (although pretty light, the Rapier has a fairly thick airfoil); But thats about the best yer gonna do...

To get any more speed than that yer gonna need more horsepower to turn more rpms with the same or higher pitch.

A 10x8 prop will just load the motor's rpm so far down that it will never get into it's peak H.P. range...