Perhaps the real differentiator between the two is the modem. The Snapdragon 617 uses a Qualcomm X8 LTE modem, with support for 2x20 MHz LTE-Advanced, with 300Mbps up and 100Mbps down. The 430 uses the X6 version, with 2x10MHz LTE-A, and 150Mbps down and 75Mbps up.
The capabilities of the modem are apparently also the last of the details Qualcomm has slowly dripped out about the capabilities of the Snapdragon 820. Here’s what you need to know: The X12 supports Cat 12 download speeds up to 600Mbps and Cat 13 upload speeds up to 150Mbps via carrier aggregation. On the Wi-Fi side, the phone supports tri-band: 60GHz for 802.11ad, plus 2.4GHz and 5GHz coverage for 2x2 802.11ac. The modem will also tap into unlicensed LTE spectrum (LTE-U), and the Zeroth modem will be able to switch back and forth between Wi-Fi and LTE for voice as well as video calling.
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