Nope, wrong again Jon2, the 625 is metal geared and faster, the 645 is metal geared and has more torque. For throttle, the 625 is perfect, and for steering either will work well, but in a RC10 gt, but a 625 will do just fine for steering, since you don't need the torque as much as you would in a monster truck.
You might want to check TeamFastEddy.com, a short time ago he had some killer deals on Hitec Servos, he may still, but I don't know for sure.
Dang it.. I am off on those servos. Thanks for that check.
TeamFastEddy did have a great deal on some servos. PM him to see what he got.