That servos specs are not great...

http://www.amainhobbies.com/product_...r-Servo-S-JR-Z

Personally yes, you could see some benefit from a faster and higher torque servo. The big question is how much you want to spend? Ball park figure for a good quality servo is gonna be 80-100 bucks, but it's money well spent..IMO

speed is a personal preference but I would want at least 180-200 oz. of torque

I run nothing slower than .10 for transit speed. It may not be needed but once you are used to driving with faster servos you won't want to go back..again IMO