In your earlier video of the steering linkage in action it appears you have about 3° of rear toe which is good for rear grip under acceleration. I would however question how it affects the rear steering efficiency. With that much rear toe I would guess the rear steering is lazy initially then would become suddenly aggressive which would cause it to feel twitchy in tight corners possibly causing oversteer after the apex of a corner. Have you tried different rear toe angles (or less rear toe) to see how it changes the feel of the car? Just curious.