If it flies as good as my Tiger2 does, it'll be excellent with the 61FX on it. The Tiger2 is a 46size and my OS46AX is just about perfect, power wise.

Since your Tiger is a 60, it ought to be excellent with the 61FX. It won't come close to ever being short of power. You would be wasting the 91 on it. Find something it's better suited for and use it there.

I wouldn't bother with the 70 four stroke. First off, you got the perfect engine for the Tiger60. Secondly, the 70FS isn't anywhere close to being right for the airplane. Would it fly it? Yeah, but you'd be wasting time. It's really better suited for 46size airplanes and not well suited for 60size.

With the perfect engine in hand, use it.