For those .25 engines you have few options:

http://masterairscrew.com/manualinst...ROPELLER2a.pdf

http://www.top-flite.com/accys/topq5000a.html

Go with the 8x6; it is still good, just a little less punch at take off's and climbing at low speeds (due to increased pitch and slip).

The low pressure ahead of the prop does not reach far from the blades.