I think that even for B&W, the circle of illumination is significantly larger than the circle of good definition, and I wouldn't say that it really covers 5x7" for B&W. If you use it carefully and make sure there is no important detail near the edge of the image circle, then I think it is possible to take advantage of that fringe area, but try photographing a church with too much front rise, and the peak of the steeple will be blurry, even in B&W, even at f:22.
That said, it is a really small, lightweight 90mm lens and not too expensive, so it's handy to have in the kit. Pair it with a normal lens that uses 40.5mm filters like a 150/4.5 Xenar or 135/5.6 Sironar, and that makes for a fairly capable and compact 2-lens 4x5" kit.