The best tire size to use (because the outer diameter matches the stock size) is 205/40-17, not 215/40-17.

You can use 17x7, 17x7.5, or 17x8 for 205/40-17 (as well as the oversized 215/40). If you have the choice, I would get the 17x7.5, since it's right in the middle and shouldn't make the tires look too bulging or too stretched.