Re: from stats, it's actually quite nippy
I updated my iPhone 5 to iOS 8 and it was noticeable faster over iOS7, and battery seemed to last longer as well. (My phone is in constant use, web, messaging, facebook, music etc)
My iPad 2 not so much, after upgrading to iOS 8 the battery doesn't seem to last as long, it takes longer to charge, but other than that no real overall difference in performance.