Apple's posted stats are 50 hours audio playback on the 6S over wire, 40 hours audio playback on the 7 over Bluetooth. I can attest that on my 7 the bluetooth can run down the battery a bit, but nowhere near as much as wifi, cellular or screen. How much battery drain you see in practice is probably affected by which headset you're using, what standards and codecs it supports, and if the iPhone can (presumably) burst AAC audio to the headset or not. I really should get around to reading a book on the bluetooth spec to better understand this stuff, though.
What bugs me about the iPhone 7 is that I expected if Apple was removing the headphone jack that they would add USB type C and Bluetooth 5 instead of the same-old lightning port and 4.2. In fact, it looks like there's more than one model of iPhone again, and the 6S' support for both CDMA and GSM appears to be a fluke, or they couldn't do it in time with the new antenna design. Unless I'm reading the iPhone LTE specs page incorrectly...
What bugs me about the iPhone 7 is that I expected if Apple was removing the headphone jack that they would add USB type C and Bluetooth 5 instead of the same-old lightning port and 4.2. In fact, it looks like there's more than one model of iPhone again, and the 6S' support for both CDMA and GSM appears to be a fluke, or they couldn't do it in time with the new antenna design. Unless I'm reading the iPhone LTE specs page incorrectly...