It depends on which pubs you're going to be playing, and how loud they let you play.
I gigged with my 100w Martamp and 4x12 on Friday night, and the master volume was just under half. It was fairly loud, but then the venue had a small stage and it's a rock pub.
In my rock covers band I use my 100w Bogner XTC and a 2x12, with the volumes around 1/4. A quieter overall sound, and we play more "normal" pubs.
I like a less pushed tone with the preamp doing most of the distortion, leaving the power section clean and tight. For me, 100w heads are where it's at and I wouldn't gig with anything else.
If you're going to be struggling for space, you may to need re-think your whole rig. A vertical 2x12 cab or stacked 1x12s may work better? You can still use the 100w head if you use Vintage 30 speakers, or something else with large power handling...