Electric tank with dual watt lower element

Can you advise how the lower element should be set? The Kenmore tank (by AO Smith, State, I believe) says, "DualWattâ„¢ lower element easily converts from 3800 watt to 5500 watt to accommodate different wiring". My electrician installed the 220/240 line for this new install of the water tank.

Someone said to set the lower element to the less wattage - it'll take longer to heat water but saves money. Or is setting to the high wattage best to keep that hot water flowing during a shower?

How do you balance the upper and lower elements - are they always to be set to the same temp (140 for me)?

Found a good answer.

Water heater safety: always use 10 gauge wire and 30 amp breaker. 30 Amp breaker x 80% rule = 24 Amps safe maximum

http://waterheatertimer.org/Figure-Volts-Amps-Watts-for-water-heater.html

A lower wattage element won't save on electricity. All it will do is take longer to heat the water. Electric resistance heat is essentially 100% efficient. All electricity used goes into heating the water for the most part. If you want to save some money, your best bet is to insulate all of the water lines (especially the hot) near the WH. Also, insulate as much of the hot water lines that you have access to. The water won't cool off as much between subsequent draws, so less water (and electricity) will be wasted.

For the upper/lower t-stat, set them both to the same temperature.