prop 14x12 / 16x8

Above is the prop recommendation right from Webra's specs for the P-5 .91.

Since I love to tinker and experimant I ran the P5 with an APC 14x12 which it turned at 8,350 rpm on Fox 5% fuel wtih 20% castor.

I then ran the 14x12 on my MVVS .91, please don't cringe Dar, it handled it just fine at 8,050.

I then tried the 14x12 on my SuperTigre .90, same fuel and it could only manage 7,000 and very quicly got hot.
I'm not sure what this tells me but I've seen several people come on here disappointed in their P5 .95 when they ran 14x6 and came up short on rpm compared to the old Webra .91s which would turn a 14x6 10.000 rpm.

The bottom line is, if you run the P-5 with a 14x12 and the SuperTigre with a 14x6 they both do their intended jobs very well. I suspect the MVVS .91 would work best with a 14x8.