I ride a SS cross bike for commuting as well as most everything else (I also have a SS mtb and fixed-gear beater/bar-bike). gearing is 42 x 18 on the crosser. works well for my hilly commute. cruising speed on the flats is a comfortable 15-17mph. SS is easy once your legs are strong enough to tolerate the mashing that is required on some uphills. I guess my only gripe with fixed/SS is that I can't go fast enough down hill...all I can do is coast downhill OR on the fixed try to keep the cadence managable.
As for more gears, the only multi-geared bike I have is an old Raleigh Pursuit I set up as a two-speed at the suggestion of a friend...front derailer with two chainrings and a SS rear. I gave it two gears to make pulling a kid-trailer less damaging on the knees
cheers.