Doesn't really matter (Score 1)

I maintain multiple ~100 core clusters and made extensive use of a few other clusters each with 10k-100k cores. RedHat, CentOS, Debian, Suse, Cray Linux, etc. They all use something slightly different.

What it really boils down to is this:
(a) Is it Linux?
(b) Are you, as the primary maintainer, comfortable with it?

If your distro of choice answers "Yes" to both of those, then you've made a decent choice.

If you end up going to tens of thousands of cores, the choice will make more of a difference. But at your scale, it's really just what you're comfortable with.