Quick note, I upgraded our two iPhone 5’s (not S’s), two third gen. iPad’s and one retina mini iPad to iOS 8. The mini was the fastest, then the 5’s, and the iPad’s were very slow.
But the upgrade worked like a charm. For each device I closed all apps and rebooted it prior to the upgrade. Now if only our 6 pluses would get here; is it October 16th yet?