Yeah I think the R50F is more of a sport engine but it seems to run good. Have not found much info on any of the Novarossis. I think I need a shorter pipe for it. I don't remember what I was getting 15k or 16k with a 10x6 and a long muffled tuned pipe. I didn't get much time to mess with it last year before winter arrived. I would like to get the R46F pylon engine but it is a little out of my budget right now. But I think a 9x8 does sound like a good prop for it.
The R28F I was getting over 18,000 with an 8x6, but I only ran it once and have not tested the 6.5x6 or 6.5x6.5 I have.