Just in case others weren't aware, there will no longer be 32 bit ISO images of RHEL or CentOS. So, you'll only have the option of 64 bit from this point forward. You can always install an older release, of course.
Here's somewhat of an explanation from Red Hat: https://access.redhat.com/solutions/509373
I'm curious how this will affect me. I've been doing a lot of CentOS based Asterisk systems. Last time I checked, Digium absolutely would not support the 64 bit version of their drivers and so it was recommended to use 32 bit if you want support. It could have changed by now, I'll have to look into it again.