A lot of the comments regarding relative volume underscore a couple of things:
First, different people and musical styles have different acceptable levels of distortion, and second, the actual power AND volume (which may or may not necessarily be related) varied according to the condition of the amp and the settings on its output tubes and their quality. Old tube amps generally ran at least 10-20% variations in performance straight off the production line. Parts tolerances were much wider and amps were set up for maximum longevity, not volume. If you had an old V4 with a crap set of tubes or one that was biased fairly cold, you'd never know what its true output potential could be. When I first got my Aguilar DB728, it was biased so cold it couldn't even reach its rated output power. I fixed that REAL quick.
That said, I agree entirely with Dave about the V4's limitations. With a loud rock band, it's SVT time ulness you like grind with not much bottom.