RE: Snapping out
Well, it may be that you don't have enough elevator, or you are coming in to it too fast. What is your elevator deflection in degees (If you can measure that)?
If it is snapping one way consistently, add in a few clicks of rudder trim in the opposite direction. For example, if it is pulling (snapping) to the left, add in some right rudder trim (leave it in all the time). Also, come in slow as I mentioned above, and add a momentary throttle burst with the up elevator input. The prop blast will keep air on the stab and vertical fin, helping to stabilize things. It will also magnify the elevator input (prop blast making the elvator more responsive). Remember, just a short prop blast as you jam in the elevator.
Try these and let me know if it helps. I found that the Edge 540 design does not do the wall as well as an Extra, or Cap (I believe the Cap is the best). Why? The wing is high on the fuselage and there is not much rudder area below the thrust line. Therefore the wing blankets the vertical stab during maneuver such as the wall.
In any case, try what I describe above and let me know how it goes.
P.S. I also think the Edge does the best torque rolls of the designs I mentioned, for the same reason (the wing and stab are close to the thrust line).