Dennis:

They are both sport engines, but the Irvine is probably a bit more powerful, as it has the BB crank and somewhat higher quality than the OS.

But in either case ditch the 10x6 three bladed prop, go with a 9x6 MAS three blader. The OS 46 FX will spin the 10x6 3b, the 40 FP wont. You can try it on the Irvine, might do OK with the 10x6 but the 9x6 3b is guaranteed to work.

Bill.