I played with some metal guys two or three years ago for about six months. Your mileage may vary--but not by much. They were loud. Everyone wore ear protection at rehearsal. (This made no sense to me--just turn it down!)
Anyway, now that I've invited everyone to get off my lawn..
Do not get a combo amp.
You want a head with 500w or more @ 4ohms. Maybe even 800w.
You will probably want 4 or more 10" speakers, 4 or more 12" speakers. In my mind, a 4x12 cab or an 8x10 cab is probably called for.
Doing this can be expensive. Welcome to bassworld. Buy used. Look for the brands providing good value: peavey or GK, etc.
It's tough to deal with the fact that any guitar player can walk in carrying a combo amp with one hand and compete volume-wise with a 500w 8x10 bass rig, but those are the facts. Guitarists with half stack dual rectifiers can basically blow away any bass rig that one person can set up.
To recap:
500w or more
8x10 or 4x12 speaker cab(s)
Buy used, avoid super cheap brands and super expensive brands
I agree - more or less.
To break it down - Ampeg SVT into a matching 810. You're done. Forever.