I highly suggest digital servos on helis and the DS285's are perfect for a T-Rex. If you have to wait to buy some of the items you need you may as well wait until May 20 for the DX7 with DS285's. It will likely be cheaper than buying the DX7 with standard servos and then buying more servos on top of that.

I have the previous veri DS281's in my T-Rex and they have been perfect, they're very precise.