RE: Thunder Tiger GP-18, anyone tried it???
A 9x6 is a good prop for a lot of 25s, but it can be a little too much load for others. I think my OS 25 FP runs better on a 9x4, but my TT Pro gets a 9x6. You just have to try, and the combination with the plane makes a difference too. Of course, there are other prop choices too.
Jim