first off, great car :thumbsup:
i don't know that i'd lower the back any more, i'd be more inclined to fit rear tyres with a slightly taller sidewall. in your last pic above it almost looks like the front's have taller sidewalls than the rear's. with a bit more sidewall at the rear it'd fill the arch more, visually lowering the car while also (imo) giving a better balance to the look of the tyres.
neil.