I can't tell you the answer, because nobody knows the answer.
I can tell you what I do and why. I turn off range mode unless there is a situation where I really, truly need every bit of range available.
My reasoning is that the tiny bit of range improvement will be made up for in a matter of seconds when charging at the next Supercharger. Thus, there is no real advantage to having range mode on all the time. Range mode optimizes battery temperature control to maximize range. In my mind this means it is NOT optimized for longevity. Probably a tiny difference, but given the tiny, usually unnecessary increase in range brought by Range Mode, I opt for possible longevity.
This spring, when driving the 225 miles in my 245 rated range MS75D between Ozona, TX and Van Horn, TX uphill against the wind with everyone else on the road under an 80 mph speed limit, I guarantee I'll have Range Mode on.