there's actually not much difference in volume between a 50w and 100w, the difference is in headroom, how loud the amp can go before the power section breaks up into overdrive. with a 100w this is later so therefore more clean volume, with a 50w this is earlier, so less clean volume.
A 50W head is probably way more than needed for pubs, as for clubs and venues, depends on the size of venue
bear in mind a lot of rock guys back used to use 50W heads over 100w heads for that very reason of earlier breakup. these days we have master volume amps and the current "in" thing seems to be daft amounts of preamp gain.
I like a healthy combo of both. however the thing with power amp breakup is there's a speaker interaction element as well. so cranking your amp with an attenuator will not yield the same results as cranking your amp without.
i would say if you need clean tones, at a pub level and small - medium club venue, 50W is still more than enough because mostly these days things are miked or Di'd direct to a mixing desk so the sound dude can carefully ensure he doesn't break the local councils decibel limits...
Could always get a lower wattage combo, they also are an "in" thing these days, low wattage rock amps.
last thing, with the amp your choosing a lot of people would say it's higher end brothers are voiced differently between 50 and 100w, 50 being more classic. don't hear it myself
