lextoy

hi all,
i have read alot and see your members are some of the more knowledgeable when it comes to wheel fitment.
i am the new owner of a 2008 535i base with the stock 17X7.5 ET 20 wheels 225 50 R17
i am looking at the TSW chicane as an upgrade
my question is about concavity, i want the wheel to be as concave as possible
so
at the 8.5 width there is the 19X8.5 ET 15 or the 18X8.5 ET 20
based on the lesser offset of the 19 would it appear more concave??
or is concavity mostly a function of the wheel width
so i would be better off stepping up to the 9.5's ,
19X9.5 or 18X9.5, even though both are rated at ET 20
i should mention i want to stay with a square setup, so i can rotate,
but the 9.5's are not rated for front fitment, do 9.5's fit in the front of a base 535i ?
my guess would be that maximum concave look is with the 9.5 wheel in a square setup
so i think i am leaning towards 19X9.5 ET20 if they would fit and look proper on front and rear of the 535i.
tire size 255 35 R19 is what i am seeing suggested but i would like as much sidewall as possible
since the roads here in philly are pretty bad, can i get a taller sidewall? or better to go with the 18x9.5, and the 245 40 R18
thank you gurus, for your advice !