The m7 cpu does not throttle as much as people think. I did the following test on my 2016 m7 rMB: I loaded the processor to a constant 100%. It took less than a minute for the processor to go full speed at 2.6GHz and 93'C. After less than a minute it started to throttle down at 2.30/2.40 GHz and about 90'C. It stayed there for about 10 minutes and than I stopped it. It took about a minute to cool down to 40'C and another 6 minutes to go down to 35'C.
Bear in mind that under normal usage you can hardly load the processor this much. Regarding battery life I think the m7 is mostly on par with the m5. I regularly get about 9-10 hours of battery life with Safari browsing and office work and the brightness at 50%. So if you can, go for the m7. You won't be affected much by cpu throttling and the battery life won't suffer.