i think you need to try them first, to be honest. To me, and I've tried the VK combo, and FA head, they sound like budget amps. They aren't bad on a budget, but you'd know they weren't amazing. I haven't tried them cranked either. I have heard some people say that the VK heads are better than the combos, but that's solely hearsay.
The one amp that's cheap (ok, two, but the valve junior doesn't count because it won't really do metal without a lot of persuasion) that I really like is the peavey windsor. It's an 80's tone, but it does have plenty of gain. I'd give that a try. But it's best if you can try all of those.