I have all three of the Schneiders, 55, 80 and 110. All of them are extraordinarily sharp if you are talking absolute resolving power. They have that slightly "European" feel when compared to the Japanese designs, namely slightly cooler colour and if my eyes don't deceive me, a touch less contrast.I see this as a plus as I can always bump my curve if I need more contrast. Remember, we are capturing 12 stops of dynamic range here. The barrels are smooth functioning, AF is fast and accurate.
Yes, they are pricey, but when they let me shoot wide open outdoors with flash, a look hitherto impossible, then to me, they are worth every penny. We are talking about roughly a grand per lens extra, right? Amortise that over an expected service life of 10-15 years and it seems worth it....
In fairness, the Mamiya D lenses are pretty awesome optically. Just be careful when you are talking about "older" Mamiya lenses. The film-generation lenses tend to be designed with a target resolution of about 20lines per mm. The current generation digibacks need lenses that can resolve 60lines/mm to take advantage of the capabilities of the back. The only "older" lens that came close was the 120 macro. If anyone knows of any others that do, I'd love to hear it.