Your get more miles on your tires if you get a square set. Otherwise, you can't rotate your tires and that means you will be replacing them much more often.
e90's typically run about 3mph slow then true speed. 63 = 60 etc.
I agree with iboost, if you went up a profile in tire, you would probably cancel out this little misnomer.
Check these out before you make a final decision to buy.
This, I think is a square set up.
http://www.ebay.com/itm/18-M5-GUNMET...67242890&rt=nc