Heater Controller - most efficient range setting

I have my Apex controller controlling my four 100w heaters in my 180g tank and 100g sump. Two heaters in tank, two heaters in sump.



I want to keep my tank at the 77-79 range.



What is the most efficient range setting that uses the least amount of electricity of a week, a month, etc:



> setting my range to 77 low to 79 high?

> setting my range to 78 low to 79 high?



Again, i'm wondering which range setting uses less electricity..... i'm sure there is a logical answer but my brain is in a fog on this one







thanks.