I upgraded my iphone 4 to ios 7 without drama BUT battery duration took a real hammering. The phone also continued to fail to connect properly on FaceTime (common glitch apparently). So I did a clean install of IOS 7 and reinstalled the apps I was using (but did NOT do a restore from backup), syncd my music back to the phone.
Wow! IOS 7 runs way faster than it did after the original upgrade, battery duration is once again great (better than it was on IOS 6) and FaceTime works properly.
So if you're having battery duration issues or your phone has slowed down I'd highly recommend doing a clean install.