I used to play my Mesa 400+ at wedding gigs...does that count?
As another who has abandoned regular heads for a pre/power setup so I could get beef in the power section, I can understand people being underwhelmed by 300w. Unless you have an extremely well designed power management system (read that as 'as good a technology as TC Electronics used to fleece people') I can't see this being much of a head turner. Even 300w micro-amps aren't head turners anymore.
Yeah, they coulda just called it 500W ...
I'm not sure why, if you want SVT tone with lots of power in a manageable size, you wouldn't just go with an SVT 7Pro.