Mike,
I've taken the opposite approach to the "twice the neg area of 4x5 and much lighter than an 8x10" that seems to be the standard answer to the question. I shoot with a heavy Sinar P2 5x7 as a field camera and really like it compared to the orders of magnitude lighter Canham wood 5x7 that I used for about a year. It's a good, stable platform that handles a wide range of lenses and, since I use lenses intended for 8x10, any possible camera movement is well within the image circle of the lenses. I use three lenses, a 150mm wide angle, a slightly long 300mm used as a normal, and a 600mm telephoto. My most used lens is the 300, my least used the 150. So, here are my reasons prefering 5x7 over any other large format:
1. I have a 5x7 enlarger and print to 10x13 on 11x14 paper. Meaning, I don't consider 5x7 a large enough size to contact print, 8x10 would be the minimum for me and even that seems small. If you don't plan to enlarge 5x7 negs, I wouldn't consider the format.
2. Having used 35mm for many years the aspect of 5x7 seems right 4x5 and 8x10 are maddingly "square".
3. I can generally shoot 5x7 at 2 to 3 fstops wider than 8x10 for the same depth of field, i.e., f22 - f45 rather than f64 to f90. With a modern lens, this results in a sharper negative. With an 8x10, I always seemed to be fighting for adequate depth of field.
4. the 5x7 groundglass is much larger than 4x5. Meaning, I find the 4x5 too small to use comfortably; the 5x7 is much better.
5 Cost of film - I've been shooting more color neg film lately. My 8x10 film costs were brushing 10 dollars a sheet, 5x7 Portra 160 NC can be bought at Badger Graphic for 3 dollars a sheet.
6. The negative size allows you to pick a film for its tonal range (most important consideration) rather than for film grain or resolution concerns. I sum it up as "I shoot 5x7 tri-x so I don't have to shoot 4x5 tmax."
Take care,
Tom