Between the OS91FX and the Saito100, I thing that the OS would be the better of the two choices. Add a power enhancing pipe and it should be respectable. It will not rocket from a hover but it will climb out respectfully and it will be lighter weight than the YS combination. I have seen the 91FX with standard muffler on the airplane and it was quite OK. The YS110 is the killer combo but it comes with the expense of high nitro fuel.

Mark