As usual it depends (and TDPs are highly misleading). First of all the 6700k is a 14nm chip, Vs. 32nm for the E5-2620. And the 6700k is a Skylake generation chip, compared to Sandy Bridge for the Xeon, which brings significantly better power-states. But on the other hand the 6700k is much higher clocked and has turbo-boost, with the latter being notoriously power hungry (can be disabled in the bios though).

In my educated guess the 6700k will use significantly less power if it mostly idles or does only burst tasks, which is actually what most self-hosters have as as task-loads. But if you serve websites to thousands of users which results in a consistently high CPU load, the Xeon is probably overall the better chip, including power-consumption under load.

Edit: I realized now that it is a E5-2620v2, which is Ivy Bridge and 22nm. So the difference is probably less, but overall the same considerations apply.

Really depends on the specific workload.

Another thing to keep in mind is that the 6700k is significantly more power efficient, especially when it isn’t consistently under high load.

Also if you do any sort of media processing the 6700k has a gpu and quicksync built in that can speed these things up significantly.