For the X1 Carbon and Yoga, due to the thin profile, you are better off with an i5 CPU. The i7 will thermal throttle under load, so while you will get better burst performance, the i5 is actually better performance for longer operations.
I just got the X1 Yoga (i5 7300u, 16GB) and so far haven't had any thermal issues with it.
I just got the X1 Yoga (i5 7300u, 16GB) and so far haven't had any thermal issues with it.