It will be very dependant on the fuel you choose and the condition of your engine. Also prop choice is very model dependant.

To keep the engine happy run it between 8400-8800rpm on which ever prop you choose. For 3D stay toward the 8800 rpm number. This will load it less and help it spool up and down faster.

A 17-6 might be Ok choice, not sure on the 18-6. But it all depends on what your model likes. Then its up to the engine and how it will turn it given your choice in fuels.

Troy Newman
Team YS