i'd say get the MM full lengths as they run from the firewall all the way back to the torque boxes, or something like that. the KB extreme matrix look pretty good, but i can imagine it might be more of a pain to install with the extra bracing. MM & FF did an install of those sometime ago. it didn't seem to be easy. i also think you need to get the heavy duty subframes to be used with that system.
either way, any decent subframes are worth it. i could feel a difference right after i installed some of KB's regular subframes with the cross-bracing (the seat felt more secure).