Huuuuuggggeeeeee impact at "cruising at 77". Its not linear power usage its more like exponential. "cruising at 60" is much much much much (much much much much) more efficient, from a power usage, not counting heat. It will take you longer to get there going 60 than 77 so not sure how that math works out, but people really discount the effect speed has on range, and it is HUUUUUGGGGGGGEEEEEEEEEEEEEEEEEEE