you can have different width rims front to back with ATTESA no worries at all. can have different offsets too
what you do need is an equal rolling diameter between the fronts and rears (left to right too, naturally)
you are correct in saying that a given tyre with a given width and profile will have a different overall rolling diameter if it is fitted to rims of differing widths due to sidewall angle. however, ATTESA has some le-way in it's design - it allows for the difference between a brand new tyre rolling diameter and a warn one and also allows different brands of tyres to be fitted front to rear (believe it or not, not all 235/40/18's fit the same due to sidewall construction etc) but i digress
i have always had a soft spot for the enkeis but i'm a sucker for good fitment (or at least better) so will say the second set as they 'fill' the guards more