Apple uses in the iPhone 6 802.11ac WiFi Plus that was released last month. That version would differ from the existing 802.11n WiFi on the iPhone 5s release in 2013 To know the difference, a video below will explain it to you.

Both iPhone speed test used in this equally been running iOS 8.0 and connected to an Apple AirPort Extreme Router 2013 release was placed 1.5 meters away from each iPhone while the iPhone connected to the AirPort Extreme uses the 5GHz-only network. No other devices connected to the network when the test is performed while the download function performed at different times.