While you're right about some schools assigning an M3 schedule (which doesn't really matter), I don't know of any school that assigns you an M4 schedule. There are two things that do make a difference:
1) When the fourth year schedule starts/whether you can push core clerkships back into mid-fourth year to get more rotations in before applications are due. I have a number of friends at other med schools that could start on their subi/away/elective rotations for fourth year as early as April. This is a reasonably significant advantage compared to those of us who are on the traditional start-m4-in-July curriculum, because it gives people who want to be in competitive specialties a lot more leeway to get in the rotations they need before September.
2) What the actual requirements are for M4 schedules. This is really a minor, minor point, but some schools have more stringent requirements than others. Ex: my school requires every student to have a medically oriented and a surgically oriented subi, versus many schools require one or the other. All that means is I'm taking Urology in April, which is a bit annoying, but no big deal otherwise. Some schools require every student to have a month in the ICU, many don't.
Either way, these are things that are pretty small on the list of stuff to look for in a med school. You could try asking the med students you encounter on your interviews about these, but unless they're M4s they will almost certainly have no idea. (This time last year, I only had a vague idea of how M4 scheduling worked at all, and I still knew more than most in my class about it)
