WI-Fi problems on iPad Air, iPad mini with Retina display and iPhone 5S after upgrading to iOS 8.
Typical results from OOKLA Speedtest before upgrade: Ping 17 ms, Upload 21 Mbps, Download 4.4 Mbps
Typical results after upgrade: Ping 39 ms, Download 2.9 Mbps, Upload 0.47 Mbps
iPad 2 with iOS 7.1.2 get 15 Mbps download and 4.4 upload on the same network.
Resetting network settings on the iOS 8 devices did not improve the performance.
Changing band on the router from 2.4 GHz to 5 GHz did give me back the speed on all devices.
However the speed occasonally...