360 Tune Up

As long as it stops creeping up, that's pretty good IMO.
In general interstate speeds (60 plus) are noticibly more work for the engine than state highways (45-55).
Not quite sure how it works out with your gearing but this extra load shows as increased throttle opening on my car. vacuum is about the same, rpm is higher.

The oil temperature is probably around the same (in the pan). Getting it around 200 is good. Helps get rid of the moisture collected.

My thinking here is that the coolant temperature is related to engine work.
It is possible that the coolant temperature is being effected by air flow, just doesn't seem like it right now.
The more work the more heat, and the heat exchange should be enough to keep the increase in check. Temps won't be right at the thermostat opening unless the radiator is doing hardly any transfer.