Don,
The biggest difference other than bulk is the use of modern glass and coatings. The Fujinon-C is a 4/4 dialyte like an Artar, so you have an idea of the circle of sharp coverage. The Nikkor-M is a Tessar, and I use a 200mm version on 4x5 and it will cover up to 5x7 sharply at f:22 (just as Nikon says it does).
Tessars are noted for being very sharp in the center of the field and sharpness dropping off rather rapidly away from center. I actually doubt whether either the Fujinon or the Nikkor is actually sharper than an Artar, but they may have the appearance of being sharper due to higher color saturation and contrast. Not to mention many lenses of the Artar's vintage have some "old lens haze" between the glasses that I think cuts contrast and apparent sharpness rather more than most people believe, mostly because they don't want to pay to have them cleaned. If your Artars are truly clean and clear without scratches, I think modern lenses don't really have that much to offer for the price unless you're going for the "calendar look" in color. And if you're scanning, the negs/transparencies from the older, lower contrast lenses may actually be easier to scan.
In these focal lengths and brands for 5x7ish, I have had a Fujinon 300C, and currently have a Nikkor 200M, a 10-3/4" Artar, a 360mm Kowa Graphic, a 360mm f:5.6 Caltar-IIN (for what I paid, I couldn't not buy it), a 16-1/2" Artar, a 19" Artar (Harley's lens), and a 450mm Fujinon C. I rather like the 200M, the 10-3/4" Artar, preferring a slightly wide (to 300mm) lens, and had Grimes custom mount it in Copal. I also like the 450mm Fuji C quite a bit on 4x5 if you have the bellows for it, and 8x10.
If you want to try any of these before you buy, let me know.
Cheers,
Steve