I tested the FC on the Optima on highway drives a number of times. At 110kmph the instant FC is 9.1L/100km while at 160kmph, its 10.2L/100km. So it actually makes more economic sense to drive at 160kmph as the FC difference is only about 1 liter every 100km. So if ure driving from KL to Ipoh, driving at 160kmph would only consume RM3.50 more compared to driving at 110kmph but ull reach faster thus your extra 'expenditure' is nullified.