One other thing i forgot to say,

i have 215/40 tyres fitted, they are toyo T1R (i think) and have the rim protector which from what i can tell is just a thick square rubber edge where the tread/side wall meet?????

You may have a few rubbing issues if you have these style tyres, this is a problem i had and why i went for the 3mm to reduce as much as possible, but i still had to trim the arches back a little

Loads of people seem to run this size without any problems tho??