I've got a saito 150 on mine, and it does fly a tiny bit "heavier" than when I had an 80 four stroke on it. I did have to move my battery all the way to the back of the fuse, and do have a small amount of lead back there (about 1 oz total), that will be replaced with a larger battery pack (figure if I need the weight, might as well go for more mah). Had I not used a pair of 225's for my elevator halves, it wouldnt have been necessary. I do have tail wires on mine (fully boxed tail), and have strengthened the landing gear block some. I also have sealed my hingelines on both sides on every control surface.
I may be able to move my cg back a little more by putting a perry pump on, and putting the tank over the CG. I'm getting 12-18 minutes on a tank (stock UCD tank), because I am hardly ever at full throttle. It will do very flat spins, climbing spins, and when i can get the sticks right, a perfectly flat knifeedge spin (meaning the fuse is parallel to the ground, rotating around the wing, without losing any altitude). Can even get it to climb like that on a good day (not the planes fault, its mine LOL). It is capable of doing pinwheels (hover to knifeedge microloop back to hover), but I've only been able to do it a few times (again, my fault, not the plane's) I'm running 15% red max fuel, stock muffler, and an apc 17/6 prop. I'll prob drop down to a 16/6 prop to see if it gives me a little faster spool up.
You have to figure given the massive amount of wing area, the weight of the engine isnt going to make a whole lot of difference. It still floats in on landing. Deadsticks are no problem (floats like a trainer, or better). Only downside is the massive amount of right thrust required to turn such a large prop. makes for a hard time aligning the spinner/cowl/fuse seams. Hence the reason I went to a dubro prop nut. No messy gap in the spinner
With the exception of the two other engines I put on mine (enya 80 four stroke, and an OS 91fx), I havent seen one within the recommended power range. There is one at our field that flies with a 91 surpass on it, but I've yet to see it fly to compare it to. The others I've seen had either an OS 120 surpass, or a saito 120 on it. Hope this helps.
Steve