It depends on two things:
1) What you're trying to optimise
2) The rim width
Obviously you want to keep the rolling diameter as near standard as possible to minimise speedo error. If you're trying to optimise cornering grip, you need to fit one of the narrower tyres that will fit on that rim width, to reduce tyrewall flexing. If you simply want to get as much rubber on the road as possible, go to the other end of the scale, although all this will give you is (perhaps) more straight-line traction at the expense of cornering grip, although all that sidewall flexing will also give a softer ride.
Andrew's Aero rides quite softly on those 225s.
For speedo accuracy, your choice is probably limited to:
215/45 (1% fast)
225/45 (0.4% slow)
235/40 (1.9% fast)