The S03T at 6V has a 60 degree speed of .27 seconds. Compare this to a Futaba 148 which has a 4.8V speed of .23 or .19 at 6V. If you feel the 148 is blazingly fast and could stand to be slowed down a little, then yes, those GWS S03T's are plenty fast, even on 6V
For 3D work, I'd be looking for a servo in the .15 - . 19 second speed, minimum.
John