It's only about the size. Here in Amsterdam stuffing myself into small and crowded busses, trams and trains, is where the size could really count. Because the 100 is deeper and taller you have to carry it higher, and further from your body. Not a problem when unloading it from a car, but it could be when you have to carry it across town on foot. Like holding a gallon of milk in front of you with a stretched arm, it gets heavy after a while. But hey, thats all theory.
I've read about the s2010 upgrade on the 40. I guess that would improve the lows as stated, but would it also take away a bit of the warm, darkbrown sound i like so much about the Rumble amps?