The amp will be putting out 100W no matter what if all is well.

that power will be distributed to the 2 cabs evenly providing they are of the same impedance so you're going to be hearing 50W from each cab
well you'd have more speaker distribution. It might be perceptively louder, but not really much.
Ibanez -> Peavey -> Eardrums

Apparently I'm on some list of people to listen to..?
it'll sound "fuller" because the sound is being projected around and more air is being moving (instead of less air moving more with just one cabinet)