DEFINATLY go with a Futaba GY401...hands down the hottest gyro out there. That gyro is AWESOME on the Trex.

And get the all metal head and tail rotor. NO slop, and its really solid.

Ive flown Bill T-rex around, and its awesome.
Im in the process of building a MX400. Im using alot of the same equipment because I know it works, and works GOOD.