Bob,

the engine to be used will be an OS 91FX. The starting prop will be 16 x 6. I am using APC at the moment but I might have other brands and types.
Manufacturer recommendation is between: 15x8, 16x6 - 8, for sport flying and 13x11 - 13 and 14x10-11 for aerobatic flying.

However, whilst reading various threads on this engine, a while ago, I compiled the following table with the prop sizes and their respective rpm. The rpm are values that various users have obtained. However it does not take into consideration the different kind of fuel or prop brand being used.

[TABLE="width: 540"]
[TR]
[TD]Prop Size[/TD]
[TD]No of reports[/TD]
[TD="colspan: 6"]Reported top RPM[/TD]
[/TR]
[TR]
[TD]13x6[/TD]
[TD]1[/TD]
[TD]12500[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]13x7[/TD]
[TD]3[/TD]
[TD]12100[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]13x8[/TD]
[TD]4[/TD]
[TD]10400[/TD]
[TD]10000[/TD]
[TD]11800[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]13x10[/TD]
[TD]1[/TD]
[TD]9800[/TD]
[TD]9500[/TD]
[TD]10400[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]14x6[/TD]
[TD]14[/TD]
[TD]10900[/TD]
[TD]10500[/TD]
[TD]10760[/TD]
[TD]12000[/TD]
[TD]11300[/TD]
[TD]10600[/TD]
[/TR]
[TR]
[TD]14x8[/TD]
[TD]2[/TD]
[TD]9100[/TD]
[TD]10400[/TD]
[TD]9500[/TD]
[TD]10200[/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]15x4[/TD]
[TD]5[/TD]
[TD]10500[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]15x6[/TD]
[TD]14[/TD]
[TD]10200[/TD]
[TD]10400[/TD]
[TD]9600[/TD]
[TD]10200[/TD]
[TD]9400[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]15x8[/TD]
[TD]1[/TD]
[TD]8100[/TD]
[TD]7900[/TD]
[TD]8900[/TD]
[TD]9000[/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]16x6[/TD]
[TD]3[/TD]
[TD]8300[/TD]
[TD]9000[/TD]
[TD]8850[/TD]
[TD]8600[/TD]
[TD]8500[/TD]
[TD][/TD]
[/TR]
[/TABLE]


I hope this table is useful for selecting the right prop for the stik.
Waiting for comments.