you'll defiantly notice a difference, a change that big will even alter your steering geometry. Whether or not you'll like it, I have no idea. I've found my Fat Franks give me a ton more grip than the Fat Boys I was using before (1.25 inches to 2.35, it was quite a change). They also give a lot more control over loose surfaces.

They roll a little slower, but not too much. Then again, I try to keep them around 55 or 60 psi. Too much lower, and they start to wiggle on me. I rode them at close to 20 (it was a slow leak that I just didn't notice), that was an interesting ride. No cornering stability, but smooth as glass. And slow as you can imagine.