Jeff,
You have already found out the issues the 28mm with have on a P45 back, softness in the corners. Enough that you will most likely have to do some cropping on most work. I have tried 2 now, and both had problems, but in different locations on the image.
The 35mm can do good work, it will not turn in quite as sharp an image as the 45mm or 55mm, but it should give you good CA free images. You may also need to try a few of them before you get one that is good corner to corner.
The 45-90 at a list around 5K, is one I will wait on for a while especially based on the results from the Mamiya 28mm also a 5K.
You also have the Cambo and Horseman solutions. Cambo just came out with a new body.
Paul C