From what I've read it looks like the GTi and VR6 got longer front arms, different ball joints, hub carriers, steering tie rods and the 5 stud hubs.
I've been looking into whether I can mix and match various parts, but I'm coming to the conclusion that I should either swap the entire plus set up over or modify the 4 stud set up.
I imagine that the only real handling benefits of the plus system are that it gives a wider track and more camber.