I happen to have some data for the Whisperflow and modeled your plumbing (60 GPM @ 30 feet) as an approximation. THe 3/4 HP full rated Whisperflow will generate about 75 GPM at 45 feet of head. Head loss goes up with flow rates and the 3/4 HP Whisperflow is actually more powerful than your pump but may not draw much more energy.
The 3/4 HP Whisperflow draws less than 1300 watts of power so for one turnover per day:
4.7 hours/day x 1.3 kwh x 30 x $.08618 / kwh = $15.80/Month
You can probably reduce than by another 30% with a two speed. Low speed uses about 500 watts but you need to double the run time.
9.4 hours/day x 0.5 kwh x 30 x $.08618 / kwh = $12.15/Month
Not much more saving but it can add up if you are doing two turnovers per day.