If it helps any, the tree point angles you need (assuming you've taken the wither template in the usual place 2" behind the back of the scapula) are based on straight lines drawn between wither and shoulder. I've used your template pic as an example. Tracing1.jpg
This ensures the front arch runs parallel to the horse's shoulder both sides and also helps show what areas are likely to need extra flocking to balance the saddle correctly (the areas between straight lines and horse's actual shape) though it depends a lot on the individual saddle's panel shape.
The newer T4s (with stitched kneepad) are slightly more forward cut than the old model (plain kneepad) and ought to be fine for both disciplines, IMO, until you get to a level where you think you need specific saddles :)