I will weigh in with another vote for the 105mm 2.5. A great lens that I have used for close to 20 years. I always wanted the 85mm but never could justify having two lens that close together. That changed when I aquired an 85mm Jupiter lens (42mm screwmount). Amazing what the slight change of focal length will do. Of course I had to buy a Fuji screwmount camera to use it, but is now my favorite portrait lens in 35mm.
As far as sharpness. That is what DOF gives you. Make those eyes dead on tack sharp and let the wide open aperture let the rest of the portrait fall away into softness.
Maybe you should look at a Mamiya 645 (or an RB67!) with something like a 135mm lens on it if you are going to do a lot of portraits?
tim in san jose