If you want high thrust, but also to retain a reasonably good speed, get a Bolly, or an APC 11x6, or an 11.5x6.
It will get 13,500-14,500 RPM and will make enough thrust to pull a 6 lb. plane vertically.
Speed will be close to a 10x6 at higher rpm.

You may need to lengthen the pipe/header, to get it into tune.