Doing a current tier 10 man is probably not going to happen. Mechanical aptitude is really necessary as the mechanics are punishing by design. Ideally, 5 is the limit on PvE as you'll want another head involved to handle mechanical aptitude and roles like healing and tanking.

Last tier or older doesn't really matter. I do BRD right now on my 5s at 90. At 100 I'll probably just run my 5s through all the Cata content I never did. So 5 is the magic number for me. The only thing I don't do much is scenarios ( I dislike these ).

You can do 10 in a LFR as those don't really matter / pretty hard to screw up.