first off, for the most part, hardcore and metal are two distinctly different things. of course a lot of the time they blend and you often cant tell the difference but there are two seperate audiences and movements.
I guess to sum it up you could say you have there two types of heavy music that come about with vastly different approaches.
now, beyond hardcore metal? what the **** does that mean? are you searching for bands that are of the most extreme sort?
if you're looking for extremities you can veer off into a few different directions I guess. Firstly I'd mention the most extreme hardcore and metalcore bands. First pick has to be Converge. A band simply insane. Check out their albums from When forever comes crashing and onwards. 2nd mention would be The Secret. Italian band in a similar vein to Converge but much heavier and darker. not as aggressive. 3rd I'd say Celestine, check out At the Borders of Arcadia, probably the heaviest thing I've ever heard. they're metalcore as well.
in heavy metal there are a few subgenres you could go by. Check out black metal like Dimmu borgir, Enslaved, Emperor, Immortal, Gorgoroth, Mayhem, Burzum.
Bloodbath is kind of old school death metal so I guess for that you'd check out Bathory, Death and such, Im less familiar with death than black though, so...
prog death, check out Opeth, really unique band.
then you could go for thrash like Slayer