Yes, that big fat wing won't let you fly fast no matter how big a motor you hang up front. More power does give the plane an added dimension, though. Saito 100 will do just fine, and won't require too much reinforcements. I put a Magnum 1.20FS on mine and went nuts reinforcing the plane, mostly on the fuselage behind the wing, where I fully sheeted top and bottom with cross-grain 1/16" balsa.

With a Saito 100, you'll also be okay balance-wise. mine needed a lot of tailweight to balance that 31.5 Oz 4stroke. I hate lead, so I sheeted the horizontal stab and enlarged/reshaped the tail feathers. I also mounted 3 servos near the tail. All that and a HD Tatone tailwheel assy finally got the plane balanced at the factory recommended point, which is correct BTW despite being much farther back than the traditional 33% chord. Mine came out a little heavy at 10lbs RTF, so now I'm gonna swap in a TT Pro120RP.

I wouldn't recommend all these mods, though. I pretty much turned it into the WM Fun World 3D, which wasn't available yet when I bought the Super Stunt 60. If I buy an SS60 again, I'd probably just do a taildragger conversion and keep it light.

Good luck and enjoy the plane. It was, and continues to be, the best $199 I've spent since I got back to RC a couple of years ago.