ORIGINAL: TLH101
I flew the original kit with an OS .91. Not unlimited vertical, but it flew quite nice.
If I decide to get the ARF, I will use the same engine.
The Kit weighed over a pound more compared to the ARF....so your 91 will easily fly this ARF and you may get close to unlimited vertical.
I have 91 as well and just got the plane. I hope it will perform well. I have to finish my 60 size Extra 300s first tho(saito 90 FA-90TS twin for the motor).