The iPhone 6's A8 processor is the second 64-bit chipset that Apple's made, and it boasts 50 percent faster graphics and a 25 percent faster CPU, which should make the phone more power-efficient. We'll eventually be able to test out these claims, of course.
Remember that co-processor in the previous iPhone? Well, the M8 co-processor gets some new sensor tricks that brings it on par with some existing phones, so you'll get elevation and air pressure readouts, and distance estimates. This is all-important for the iPhone's fitness apps.
Apple never gives battery specifics in mAh, but the iPhone 6 is rated to last up to 10 hours over 3G and LTE, and up to 11 hours on Wi‑Fi and video. There's Wi-Fi calling at long last, and Voice over LTE (aka VoLTE). Speaking of LTE, new specs allow for a theoretical zenith of 150Mbps downlink.
Support for the Wi-Fi 802.11 ac standard means you're looking at Wi-Fi speeds three times faster than those in the iPhone 5S.