I went to update my system, and noticed something interesting. Yum, while rebuilding the rpms out of delta rpms, gives a bandwidth meter on how fast the operation is going, and as it turns out, yum is slower than just pulling random packages from the internet. In some ways, running Presto actually slows down updates when a fast connection to the mirror is available. It stands to reason that in any network running a local mirror, Presto is probably not needed either.
So do i keep Presto enabled? For the time being, i will. The extra CPU time costs my employer money, which i'd rather do than use up someone else's bandwidth. While we're probably talking fractions of pennies here, with the number of Fedora users, such things do add up.