I suspect you won't find a faster one than this, if you hook it directly into your lipo. Price isn't bad, either - worth a punt, maybe? Out of stock, mind.
Mi Digital High Voltage Metal Gear Servo 8.40kg / 0.03 / 61g
- Voltage: 6.0v / 7.4v
- Speed: 0.04sec/60deg (6.0v) - 0.03sec/60deg (7.4v)
- Torque: 7.00kg.cm (6.0v) - 8.40kg.cm (7.4v)
- Size: 40.1mm x 20.5mm x 39.4mm
- Weight: 61g
- Gear Train: Full Titanium Alloy
- Motor: Coreless
- $35.69