I was able to compare and contrast the install times for a machine registered to Spacewalk vs one registered to Foreman while installing glibc
Both took the same amount of time.
I have noticed that yum commands are infinitely more responsive after adding more time to the metadata_expiration value however. Unlike manually editing redhat.repo, the subscription-manager command actually sticks.
I was able to change this all of the repos my test machine is currently subscribed to, but I fear this will be a recurring maintenance issue for us as we will have to make this change for each additional repo a machine is subscribed to.
I know this appears to be hard coded in Katello as a default, but I wonder if there is any way we could set a new global metadata expiration timeout value