I've done gigs with my medium-loud 8-pc 50's-60's-70's band with 3-member horn section doing rock, pop, and R&B with as little as a 25w B-15 from the 60's and a 35w BA110 practice amp with a single 10". We do everything from gigs in small rooms to outdoor gigs in front of thousands, and I've been able to pull it off. When things start getting loud onstage, they get a little distorted, but in a good way so it was cool. But for staying clean, I like a little more power, so I upgraded the BA110 to a BA112 v2, and that's 75w. I can pull off clean tones easily with it without any danger of pushing it into the red.
That said, I like the big stuff MUCH better and often use bigger rigs just because they sound bigger, but I could probably pull off all my gigs with the BA112. Maybe not the hard rock gigs, but I don't get a whole lot of call for them. Would like to, though.