The Z550 comes with the XS3 and has around 80oz of torque, this is from memory so I may be off a little. You could go with a Hitec MG645 that runs aroudn $50 and has 130oz of torque, again from memory. But the Hitec is a good servo, I use this one (645) with my XS3 radio in a RC10GT and have been very pleased.