I use those same tanks with a pressure switch setting of 100/120. As long as the air pressure is just under the pump start pressure, you won't over stretch the bladder. Bladders are busted from going up and down like bending a wire till it breaks. This happens as the pump cycles on and off. "Normal cycling" means the bladder will last an average of 7 years. "Over-cycling" will cause the bladder and everything else to wear out sooner. The less cycling, the longer the bladder and everything else will last. The higher the pressure setting, the less water the tank will hold. At 40/60 that tank holds about 23 gallons, at 48/68 it only holds about 18 gallons, that is what causes more cycling.