RE: DA-85/ Extra
It's really going to depend on the weight of the plane and how much 3D performance you require.
The 85 is going to save you over a pound (and some money) so if the plane you are looking at comes in 27-28 pounds with a DA 100 stock.. you could get an 85, spend some money on CF tubes and probably be close to 26 pounds.. 85 will fly that well.