Did a clean restoration to IOS 8.0.2 with iTunes yesterday. Safari on iPhone 5s running 8.0.2 is still considerably slower than our iPhone 5 running 7.1.2
There are times when pages load halfway, freeze and network activity circle just spins.
Updated to 8.0 OTA just fine, and updated to 8.0.2 through iTunes just fine (the only minor issue was restoring my backup - had to use the one in iTunes because I couldn't figure it how to get to the iCloud one in iOS 8).
I did an "upgrade" on my iPhone 5s from iOS 7.1.2 via iTunes using the iOS 8.0 GM release back on September 9th and haven't had any performance or battery issues.
Not a surprising question coming from someone with a 64GB iPhone. At least for me, doing the install OTA required at least 4.2GB of free disk space which I do not have and I refuse to get a higher capacity iPhone just so I can update the software via OTA.
I did an "upgrade" on my iPhone 5s from iOS 7.1.2 via iTunes using the iOS 8.0 GM release back on September 9th and haven't had any performance or battery issues.
try doing a real time comparison with safari on your iphone 5s to safari on an iphone 5 running 7.1.2 , it may show you performance issues. My iphone 5s runs safari slower than our three other iPhone 5 that are still on 7.1.2