Just worth considering the speedo.
As you know standard tyre size is 205/45/17, and on 215/45/17 you would be doing 71 mph where you would have been doing 70 on the narrower tyres on the same speedo reading.
We all know the speedos are not 100% accurate but just something to consider.
http://www.alloywheels.com/tyrecalc.asp
How does that work out? as you are are not changing the overall diameter of the wheel and tire you are only changing the width of the tire?
The profile of a tyre is the percentage of the width. i.e. 45 profile is 45% of the 205mm width. Go wider but keep the profile the same, you change the profile and therefore radius by 45% of the change in width.