not an expert, but a personal perception:
i've had nothing but solid-state 60-watters back when i was actually in a band rehearsing situation. i've never felt a need for more power, although my last amp was Tech21 Trademark 60, which I often ran into the PA, but for more presence, not really volume. I liked it going through more speakers.
that being said, after sampling the 5wt Epi Valve Junior at Sam Ash i felt it's actually louder - i was actually afraid to turn it past noon - they would kick me out. And if you run it into a multiple speaker cab or mic it, really volume will not be an issue.
in quantitative terms 5 watt is about half as loud as 50 watt (it's exponential - 10x wattage to double perceived loudness).
getting a stack or a powerful combo will actually cause problems - being too loud, as in drowning out the bass and drums and still not really sounding the amp's best.