Depends what offset the 8s are
I've got 17 x 8 et 35, 205/40/17 tyres which give a slight streched look, no rubbing at all on std suspension. i think you'd get away with 215/40s tho
the rs4's are prob a lower offset
sisson is urs decked mate?
Nah thats lowered 40mm at the front and around 65mm at the back.