depends if you play games or not, lots of people have benchmarked things like BF4 as 15-30% faster under Win8.1 with a lot less lag spikes. Nvidia drivers etc are all optimized better under Win8.1. Under the hood Win8.1 does a lot of stuff better, especially with things like SSD drives and UEFI booting. Its all of course balanced by shitty metro, but honestly with classic whatever config and Start8 (or pokki) I don't see a difference at all between my 8.1 and 7 in terms of day to day use. Sometimes you get that goddamn Metro full screen window and you rage at your PC for a few seconds, but life goes on.
Whats hilarious is my parents PC has win8 too (new PC this fall) and for a week my dad literally would restart the computer every time he got trapped in the metro screen, since he didn't know how to get out of it. Fortunately with 8.1, if you choose the go-away-metro stuff you rarely see it anymore.