I mean, if everything is exactly identical, then sure 5 might be better than 10. I could list 100 other things (not exaggerating) about a school that I would find more important than whether there are 4, 5, 6, 7, or 8 people to a cadaver. Some schools actually don't even have dissection. That would be a more important theoretical question to ask if you were concerned on whether they had dissection or not.
USMLE prep time is probably going to be adequate for nearly and US MD school. All schools want their students to do well on the board exams. A couple weeks difference here or there, in my opinion, shouldn't really influence your decision too much.
Your question is really better suited to a new thread (or one of many that have been posted previously), but briefly, my top 3 things to try to ascertain about a school before attending would be:
#1 Strength, availability, and flexibility of clinical rotations
#2 How supportive are faculty and administration of students (My school goes above and beyond in this category and it is a-m-a-z-i-n-g.)
[unfortunately, these can be hard to figure out as a pre-med with limited time at the school--second looks are a good time for these]
(not quite as important)
#3 Resources and protected time for research
Unranked p/f is a cherry on top.
Edit: These assume school location is acceptable to you.