I have a variety of lenses for my 5x7 cameras. In the normal range, my favorite is the multicoated 210mm/5.6 Fujinon NWS plasmat, with outside lens barrel lettering. This used lens is inexpensive, very sharp, and with excellent coverage,although physically large like all 210mm plasmats. I also use and like the older but very sharp 203/7.7 Kodak Ektar, a Dialyte design process lens that's small and light, but not much coverage beyond the minimum required for 5x7. Supposedly, the 203/7.7 Ektar was a favorite of Ansel Adams on 4x5. It does cover 5x7, though barely, and most Kodak Supermatic shutters defiinitely benefit from a professional CLAC.
240mm-300mm lenses probably best fit your described needs. Of those, I would agree with the earlier poster that the early single-coated Fujinon 250mm/6.7 W plasmat is one of the better ones. I got mine for under $200 plus shipping and it's very nice. Also suitable, are 240mm and 305mm f/9 G-Claron plasmats and 305mm Repro-Clarons Dialyte-style process lenses. All are nicely sharp and also small enough to work with most field cameras. Many people swear by the 300mm Nikkor M or 10 inch and 12 inch Commercial Ektars. These are Tessar-formula lenses.
Some older lens designs like Dagors and Zeiss Protar VII work ok, some very well. But, there is more sample variability among those older lenses.
I can't really comment upon soft-focus lenses. They're just "not my thing" and, although I have one or two lenses that are soft-focus, I've never bought one, at least not intentionally.