i started out with a 36. it worked great for me, but i'm 135lbs. pulled hills fine, ran great.
i'm now running a 32, and it's fine for me too. a little sluggish going up hill, but there's not many hills where i ride. on a long straight, i'm hitting 40-43mph. cruises 35 easy. not too bad off the line, either, and it cruises through slow parking lots no problem. maybe i just got a super-deluxe special engine, 'cause everyone else is gonna tell you different.
my 24" rustoration bike i'm building is gonna have a 30 to start with. i've got a 28, too, but that's about the limit. any smaller and there's no clearance between the wheel, the hub and the chain without doing crazy mods.
my 26" seems pretty maxed out as far as gearing goes. anything lower is gonna bog up hills, and take a long time to get up to speed.
a 28 would work great at bonneville, though. you'd have plenty of time to get to top speed.