I've just picked up a Mark V 35 and I won't be using it with my band anytime soon, but I am curious how the 4 EL84's hold up at band volumes?
Are you playing a large room with a beast of the drummer who just can't/won't hold back?
Are you sharing stage with another guitarist who's always pumping 50+ watts through a 4x12" cabinet?
Is your band exclusively loud and aggressive metal with no compromise for venue or personnel?
Situations like that, and you'll wish you had a little more oomph. Not
much more, but if we're being completely honest... you'll wish you had a little more.
Any other situation, however, the
vast majority of situations, and you should be more than fine. For me, the Mark V:25 was more than enough except on a few heavier songs. The V:35, even in 10 and 25 modes, has more body, especially in the mids (well, at least mine did), which is great if you want your guitar to be heard in the mix.
And of course, if you are mic'd up to a halfway decent PA, it'll never be an issue anyway.
I hope another rock/metal guy will chime in and confirm/deny 35watts is loud enough.
Unfortunately, there is no clear answer; it really depends on your definition of "metal" and who you're playing with. It
definitely will be enough for most situations, but if you want to be 100% sure, I'd suggest finding a used 90 watt V.
So consider your context.
For me, it'd absolutely be enough. But I'm the only guitarist, while my "metal" drummer has a strong jazz and funk background, is a great listener, and is able/willing to dial things back just a touch if necessary. On the other hand, there's a band (two guitars, bass, vocals, huge kit) I hear practicing in the unit next door each weekend that literally shakes my walls.
If your context is similar to mine, a V:35 would certainly be enough (more than enough, really). But you'd have issues keeping the V:35 afloat in my neighbor's band, especially the lower frequencies.