I have a VH-4, and I can definately say that it will do metal with great ease. The real question, though is what type of metal do you want to play?
THe VH-4 is very tight and very focused. Channel 3 will deliver early VH tones, and modified Marshall late 80's LA Hair metal tones, but with more bottom end chunk and a much tighter focus, with more gain on tap.
Channel 4 will give you really knarly, fuzzed out, compressed death metal tones, albeit with very tight focus and lots of bottom end.
Channel 2 will yield heavy bottomed early Marshall style tones, again with very tight focus.
If you're looking to play sludge/ stoner metal like Sleep, you can still use a VH-4, with caveat that it will NOT have the loose and juicy damping that an old Orange or Matamp will deliver.
Although I've not tried the other models, other people say that the Einstein is a little bit loose than a VH-4, and a Herbert is looser still.