So playing thrash metal, with two guitarists (mesa 412s), and a loud drummer, Ill be ok with the walkabout and two 8 ohm mesa ph410s?
No one can know for sure without trying.....depends how much the 412s are cranked.....and if the guitards and you are battling for the same band of the freq spectrum....and whether you are using enough distortion to muddy your mids.....and whether you're cranking lows and sucking up a lot of output by doing so...... For any "reasonable" group I'd say you'll be fine....but not all groups are "reasonable".