AT shifter (S) mode preference.

Started to play with the (S) mode shifter position in 4 and 5 and curious what is the best value for city/street drive and freeway.
In 4 at 45+ MPH the tach is at 2000 and a bit more. Should I keep it in 4 or bump it in 5?
After 65 on freeway I put it in 5

 

I personally like S5 in town and go to 6 on the interstate. Even in S5 it tachs up more going through the gears than it does in D. Due to the mpg loss over 65 I use 6. I am in total flat land here if that makes a difference.

 

I understood the point of using the (S) mode is to limit the gear hunting by the AT and force the AT not to use the 6th gear. In that case, why I need to manually put it in the 6th gear? since the AT does it automatically?

 

On the interstate, over 50 mph, I use D. I have no hunting or shift issues. I just limit it to S5 in town because it will jump into 6 at 45 mph.

 

S5 for most city and highway driving, towing my camper I go down to S4. I very seldom use 6th gear.

 

What is a better choice (for engine and tranni) to put it in (S 4, 5, 6) or ECT?