I know "wider is better", but is the benefit more of a consistency and stability thing, or are there 60-ft improvements as well?

With 275/60R15 on the old car, I have these wheel width options:
- 8", which is what I ran before; the original M/T ET Street Radial seemed very sensitive to tire pressure and worked best at 17.5 psi for me
- 9", never tried, but would fit OK
- 10", never tried, but mocked it up and it's a tight squeeze on my car between limited leaf-spring clearance and slightly trimmed inner fender well lips

Thx