I can play metal with my Classic 50 with no pedal, no problem. BUT, the amp is insainly loud! I can come close to, if not completely, drowning out my drummer with that amp. Next to a Classic 50, I doubt you would even be able to tell that 212R was even turned on at full volume. I can send you some clips of my C50 doing the metal thing if you want, but it might be a week or two (it's at my drummers).

The Valve King is not even out yet, so nobody will be able to give you any opinions on it.

The Marshall, however a good amp, is overpriced for what it is.

Of the three you listed, the Vox would probably be your best bet.

Have you taken a look at the Line 6 Spider II series? I've heard a lot of great things about them, but don't have any personal experience though. I think one of these or the Vox would be a good choice.

Hey, if you order it through MF you can alway's return it if you don't like it.