Just a suggestion, but you might look at a 120mm f5.6 APO-Symmar before you commit to a 90mm. When I was playing with a 6x17 back on a 4x5 camera, the lens I found most useful was a 120mm f8 Super-Angulon MC with its Schneider center filter The 90mm lens I used with it, a Super-Angulon XL, which I did not have a center filter for, was too wide and had too much of a hot spot in the center.

While I know the 120mm Super-Angulon covers, if I were to play with this again, I would try the APO-Symmar. Slightly faster, smaller and cheaper; it should have less fall off and still have plenty of coverage for an application that did not require any movements and would not need a center filter.