Actually I've flown my GP Big Stick .60 with both a TH .75 and an OS .91 Four stroke.

The Tower Hobbies .75 beats the OS .91 four stroke in terms of power on this plane.

I ended up leaving the .75 on the plane as the performance is much better.

And this with 3800 NiMH batteries in the plane on both instances, to permit me to fly all day long w/o interruption.

It penetrates wind better with the extra loading.

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BTW: I also have a .91 Four Stroker on my Skybolt, and there is another club member at our field with the same plane and the T.H. .75 engine. He gets MUCH better performance on his Skybolt, though mine sounds more authentic.