It's funny you should ask that question.

I had a Super Skybolt ARF and flew it first with the OS .75AX and later with the OS FS .91 Surpass II.

Both engines are almost identical in terms of performance.

The .75AX spun an APC 14x6 at an even 10,000rpm.
The FS .91 spun the same prop slightly less at about 9,800rpm

They are both a good match for the airframe. The 4-stroke sounds better.

Both engines have plenty of power for aerobatics but neither engine will give you unlimited vertical.

I also tried a Saito 1.25 and it was probably too much power, but it sure was fun.

The Skybolt is the model i wish i never sold and i'm now considering getting another.

If I did i would definitely go for the OS FS 1.10a or maybe a Saito 1.00 or 1.15

If 2-stroke is your thing, then the OS .95AX would be better than the .75AX.