I have updated 3 boxes from FC5->FC6 (x86_64) using anaconda (booted from a DVD).
Update time was ~90-120min depending on the sys.
It feels like there is a quadratic algorithm somewhere, plus slow database operation (non-cached, or poor transactions): http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=208725 http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=208717 http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=209323 http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=208726
Also, mere package install itself can speedup by a factor of 5: http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=71184