Would the Razor Yak work WELL with a saito 91? I dont want it to struggle. According to my "calculations", the engine should put out 11lbs of thrust.

What do you guys thinks?

91 is fine. You would probably like a 100 on it better but it won't be bad with a 91.
If you've got the engine then use it.

agree, use the engine you have to start with. If you ever want more power then you could always upgrade.

I have both, but the 91 is currently not mounted in a plane. Ill give it a shot.

Thanks.

how well will an OS95AX work on this model? Enough engine for stupid pullout power at Colorado elevations (5280 ft)?

Im thinking a 95ax should be equivalent to about a 140ish 4 stroke. They recommend a 100 4 stroke, so that should be plenty of power.

Correct me if im mistaken

If it were me at a mile high, I'd go with a YS110, or a 120AX or Saito 125. If you don't already have an engine, that's where I'd start.
The 120AX is only an ounce more than the 95 and if you want stupid power, there it is.

Just keep in mind that weight is just as important at high altitude as having enough power.
The airframe acts like is has less wing area along with being heavier.