When the iPhone 5 first came out, one of the major disappointments for me was that it didn’t have 802.11ac. 
Among the many new features in the iPhone 6 is that the Wi-Fi interface has been upgraded to 802.11ac.
Why is this important?
First up, it’s just plain faster.
The maximum speed of a single-stream 802.11n device is 150 Mbps, and that is in fact what the iPhone 5 supports. With a 40 MHz channel and short guard interval, the best you can do is 150 Mbps. A single stream 802.11ac device operating in an 80 MHz channel can do much better than that, with a top speed of 433 Mbps.
What does this mean for you? It’s likely that the iPhone 6’s Wi-Fi link is no longer the weak link in the data path to its server. (If it is, please help me get connectivity like yours!) In addition, the increased capabilities of 802.11ac reduce the iPhone 6’s demand on networks, helping any network it is attached to. I wrote about this in an article published in Wired last year, Why 802.11ac Helps Every Network.
Almost as importantly, as we’ve said for some time, 802.11ac improves range, and more importantly, the data rates at higher ranges.
Compared to 802.11n, an 802.11ac AP should provide better quality coverage. Just as 802.11n was sometimes called “better G than G” in reference to the many ways that it improved the performance of older 802.11g, get ready to experience how 802.11ac is “better N than N.” Every generation of Wi-Fi chipset incorporates all the lessons learned from everything that has come before, and typicallyoffers improved performance, especially in the challenging long-range operations. Some 802.11ac APs (including Aerohive’s AP230) are able to support transmit beamforming to improve signal quality. Finally, 802.11ac is mainly a 5 GHz specification, which improves speed by using cleaner spectrum.
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Read more blogs on Apple's iPhone 6 and iOS 8 announcement:
iOS 8 upgrades threatening your WLAN? Let AVC throttle traffic
iPhone 6 + iBeacons + Wi-Fi: In-store shopping ups its game