The 4*40 can hover on a .40 2-stroke. a .72 4-stroke is recommended for the 4* 60. (the O.S. .72 4-stroke has as much power as the O.S. .61 FX)

On my 4*40, I used a Magnum XL .40 with a APC 12.25 X 3.75. The Magnum has about 85% to 90% of the power of a O.S. .40 FX, or about the same as a O.S. LA .40... that is enough for unlimited consecutive inside-outside vertical 8's. (See AMA Pattern maneuvers) Only reason I fell out was a dumb thumb, not a lack of power. With that prop it will accelerate going straight up and is capable of any maneuver in the AMA intermediate Pattern. (and most fun-fly maneuvers) Anything the airframe was designed for... thats all the power you need.

I litterally wore out my 4*40. Went to do a recover job after 15 months of flying it and found I'd overstressed the plane beyond reasonable repair. (and some fuel soaking from bad seams on cheap covering...)

By the way... you want the low pitch prop for landings. With a 10X6 it wouldn't slow down enought to stick to the ground with the engine at idle. An 11X4 (cheaper and easier to find than the 12.25X3.75) and it slows down fine (and has almost as good vertical performance). The 4*40 is not meant to fly 120 mph... so the low pitch is a VERY good thing.