Deore was in and out like many component names. Around 1995 it went something like XTR, deore-XT, deore-LX, STX-RC, STX, then maybe acera followed by altus? not sure. Later deore became a group on its own again which fell just below LX... today LX has become a touring group and has been relaced by SLX in the MTB line-up.

Dsm Berg, I suggest you source an 8 speed derailleur from that period in the STX-XT range. I would say the XT is the best for all around value. XTR is sweet, but I wouldn't put one on unless I got a real good deal on it. It might be a tad lighter, but you won't notice much difference even from the STX, those 8 speed derailleurs were awesome. Stay away from the 9speeds, I don't know what they changed by in my experience I see more pooched 9speed XT and deore derailleurs than I do 7/8speed... I also find that the 9 speed just don't shift as well on 7/8 speed systems as the originals... I got a new deore 9speed shadow and tried to set it up with 8speed ultegra bar-cons and it just didn't work as well as the old stx/acera style derailleur I have (once the sticker is gone its hard to tell the difference unless you check the part number, but I don't care enough to do so).