Hi PHK,
I'm not a concert shooter, but have some experience with longer lenses. If an MF 80-200 2.8 is under consideration, I'd take a look at the Tamron SP 80-200/2.8 Adaptall 2, which is IMO the best of the fast xx-200 MF zooms. This is an excellent lens -- one of the few zooms that stand up to pretty critical use with the P F 1.7x AFA for birding. I got mine for @ $212 a few years ago, but the asking prices seem to have gone up since, and you'd still have to get a PK/A adapter which can now be a significant expense. It's hard to compare them, but I'd say you'd get similar optical performance to your excellent A70-210/4, at a stop faster, but the size/weight penalty is significant, as it always is with fast tele stuff. If you could get lucky and find one cheap, this Tamron would be a lens to consider.
http://www.adaptall-2.com/lenses/30A.html
It's probably not an option because of the money, but something to think about if you shoot a lot of low light stuff, the better high ISO performance of the K20 or K7 CMOS sensor gives you more latitude shooting slower lenses in lower light situations. Your A70-210/4 would shine with either of these bodies at higher ISO without having the size/weight penalty of the faster glass.
A last option would be to just bump the ISO up another stop and look for a good NR program. I'd take a close look at Topaz Denoise. It's kinda slow, but does a remarkable job reducing noise while retaining finer detail.
Scott