I tried in vain to find info on the rs-b85. I'm afraid I can't be of much help on the quality of it, except to say that I have been impressed with the sound quality of some of these technics machines from this vintage. I haven't paid any attention at all to model numbers.
What will end up I think being the deciding facter I think is whether or not you are able to optimize the azimuth and do it easily. One think I should mention is that on at least one new technics deck it left the factory with it's azimuth so far off you could visually see it. So note that it may not only be horrendously off, but so could the deck that the tapes were recorded on. (this problem of the azimuth being off on decks from the factory is not unique to technics, and is actually more common than not on mass market decks).
When the azimuth is off, the highs roll of at an accelerated rate, the phase characteristics kill the depth, and the sound becomes dull and congested. If you are using dolby, the problem multiplies as the dolby playback is then trying to recreate the sound of something that is out of phase with what was recorded.
I would suggest trying to find the azimuth adjustment screw on your deck, it is the adjustment that controls the head's angle in relation to the tape travel, the head should be at a perfect 90 to the tape. you should not be able to see any error, but you might be able to identify which screw would be able to adjust it. Play a tape, and listen to it as you turn the screw. take care to note the position of the screwdriver, so you can get back to where you started if you have to. count how many turns or half turns you make in each direction as you hear the sound degrade, and then count the turns to the middle of that. I highlhy recommend having a pencil and paper handy as you do this to keep track. write down where you are at in relation to your starting point as well. This is the laymans way to do this. It works, you just have to be careful enough as you do it to keep track of where you are at.
If it seems to complicated on the technics machine, then the 480 would be a worthwhile way to go. It has toothed gears on the adjustments, so you can count the 'clicks' as you go. It is also clear which one is the azimuth adjustment.
The azinuth adjustment really is the most important one, and the deck that plays with the correct adjustment will always outperform any that is out. The nak dragon, the king of all naks, actually continually adjust it's azimuth automatically. the dr-1 has a nob for the user to adjust by ear. Some of the older nak's, the 680's self adjust the record head to match the play head. Note that for playback, it is not ideal to be at perfect adjustment to the tape travel, but to match perfectly the head to what is recorded on the tape.
Good luck.
