Help me choose an affordable 85mm that's sharp at f2.0

Given the continuing absence of a fast medium-tele m4/3 lens, I'm looking for an 85mm (or at a stretch up to 100mm) legacy lens that will be sharp at f2 on my GH2.

There are affordable FDs and Nikkors, and somewhat less affordable Rokkor-Xs and Zuikos (my limit at present is about $400). Then there are the Rokinon/Vivitar/Samyang clones, which get good reviews.

I've tried one of the above so far (I won't say which one just yet) ... at f4 it was equivalent to my 45-200mm Lumix, but at f2.8 and f2 it became much softer.

Any suggestions or should I just resign myself to shooting with the 45-200 with the ISO cranked 2 stops? Oh and .... I do know the 35-100mm Pany is on it's way, but it won't be f2 and I'm sure will be at least 2-3X my present budget.