Several years ago when I was looking for a 90mm M lens there was a lot of praise around for the Summicron-M pre-asph (E55), and now in this thread it has hardly received any attention. It was praised for sharpness above f2, with a slightly more "flattering" look for wide-open portraits, and that's exactly what it does. Beautiful lens. It's a big chunk of glass, especially compared to the diminutive Minolta 90/4. For travel, the latter is perfect. For all else, the Summicron is hard to fault.
Steve