For the Wraith, which is not a speed machine if my intel is correct, the WR-7701 will be perfect. It will have massive torque, if provided with enough power. A small tip would be to get a Castle Creations 10A BEC and programming kit for the BEC to ensure the servo will have a nice steady 8.4V supply.
you won't be sorry.

That's what I have done to ensure my WR-6601 get's a steady 8.4V supply in my Durango DEX408 buggy. Not as fast as the WR-4401 but more powerful.

I have the WR-4401 in my Hong Nor Nexx8 buggy, which i'm getting ready for some fun. A CC 10A BEC will be installed in that as well. Ensurering a steady 6.6V power stream, so I will get maximum steering torque.