Tests showed when the Hitec HS-311 was at 150Hz & buzzing, it sucked 900mA.  At 100Hz, it didn't buzz & dropped back to 200mA, so definitely check the PWM frequency.  Still, a brushless servo would get the ultimate range.  

An 8.35 mile drive with nothing but a speaker & no headlights burned 3200mAh or 383mAh/mile.  Still far below the good old days.  Steering was rock solid with P 200 D 200.  D had to be a bit lower without the camera.  Range anxiety makes it difficult to replace with a larger vehicle until the source of the increased burn rate is known.  The ideal vehicle would go 30 miles using 13500mAh.