Bearing in mind Steve doesn't want to cut the arches as he has already stated.
Put it this way a 235 tyre with an et25 rim, would defiantley foul the arches,I know Justin had this set up on his white 3dr and had problems with the tyre fouling the rear arch,his car was fitted with fairly new Koni and Ahmed springs at the time.

I had a 235 tyres on my last 3dr with the cxns and they were an et35 offset,arches were trimmed but the tyre did contact the front end of the rear arch occassionally.
I think if you had coilovers fitted you are open to more options as there is so much more adjustment with ride height etc than on the Konis.

Why not just try a 6mm spacer on the wheels you already have just to see what it looks like or be brave and try a 10mm spacer, just to see how it looks and if you get any fouling issues once driving the car. You won't get any problem until the car squats when it comes on boost then that will tell the true story.Stick with the 215 tyre as the arches are uncut and you have the Konis already fitted up. It's a minefield Steve,trial and error I'm affraid.

CheeRS.Lee.