with the OS 120 you looking at about 95-110mph. we have a one at our club with a gms thats been tuned up some and its just barely hitting 118-120. the best prop for the GMS has been the 15x7. for the OS I would work on getting the the most out of the 15x8.

I have the OS 120ax in a H9 p-51. I have the pipe on it. the 15x8 is the fastest but I dont have the pipe optimized for it yet. I was supprised to find out that the OS turns a APC 16x8 at 9,800 though.