To just say use an IO-540 is a bit of a simplification as there are several models of Io-540s that put out 300hp very reliably. PA-32-300 is the prime example.
Thanks guys, I have seen the video of the 10 with an LS1 that can get 6000 fpm climb. I am certainly not wanting to go there. But I have seen a few references to 10's being able to comfortably handle 540's over 300 hp. If 260 is the manufactures recommended max then that is where I will say. All input is greatly appreciated!!
It's all opinion but I would also agree that 260 is the sweet spot. Flies fast at altitude and burns about the same as an SUV MPG. This pics are with a 20 knot tailwind at 13500.
Andy, IO-540's can be made to develop near 400 HP but my 260 HP -10 is faster than a friend's 300 HP -10, because I have the two-bladed Hartzell blended-airfoil prop. He has a three-bladed composite prop and is around 7 knots slower.
250 to 260HP is just fine for this aircraft. Just fine until your buddy, with the same prop and 20 more HP walks right by you one day. Or worse yet you have to ask him to throttle back a bit when you are on a cross country!