Your use case scenario may be different, but I don't find any major difference in speed between 802.11ac and 802.11n when using the iPad Air 2 as a media consumption device.
Ditto.
Anyway, I can safely say that the iPad Air 2 and the iPhone 6 Plus makes *FULL* use of my internet bandwidth (see screenshots) which is a 100Mbps cable connection

... pity my cable's max upload speeds are a bit weak-sauce though.
Overall, the iPad Air 2 is extremely speedy for example, I just did an update of 4 apps totalling about 185MB and they were downloaded, installed and ready to be used in less than 15 seconds total.