Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I've been running iOS 7 since beta 1 on my 4S. I have no issues at all with speed.

got it running on my 4S, seems fine, and I saw some tips on turning off a few things if I want more speed and battery efficiency, but for now all A-OK! except I hate the new Reminders app. That app has been ruined for me.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.