what do you mean by matching the cabs?
I think Jimmy and KsPiNeSh meant two exactly the same cabs from the same brand (and perhaps even the same configuration of speakers). I don't actually know why mixing cabs isn't so good, but some guys here can enlighten that.
To me matching cabs just seems logical.
The 700RB is a very good choice for metal. I am gassing for that one too.
I like this solid-state powerhouse (yes, I know they even have 2 bigger) because to my taste I like the basstone in metal to be more brighter, colder and clean.
In this thread I've seen a lot of lot for Mesa. Not what I personally would go for but ideal if you want some more grit and grind from your amp without using pedals.
My cab choice for the 700RB personally would be Eden 4x10", 2 of them (1 would do for practice and the smaller gigs). I actually had the chance of playing an 700RB through an Eden cab once.
Best cabs I tried so far in the 4x10 department.
If for reasons unknown to me

you like 2x10 cabs, go with that.
They are not "weaker" than the average 4x10. Depends on your whole setup.
And if you can afford 3 cabs that would save you some transportation. 1 at home, 2 at rehearshal, so you only need to carry your head. Just an idea.
And to repeat what everyone said: any amp/cab can be used for metal, if tweaked right. If I'd had to go on budget-amplification for a metal rig, I'd even dare to go Ashdown MAG.
Even, Eden wich are not that common with metal bassists are absolute beatys to my ears.
Their cabs I really want. To bad they are so expensive.
Good luck with your choice.
edit: I'm a slow typer, KsPiNeSh beat me to the answer.