Ahhhh Grandlines. Well done to you for getting them.
They were my dream too, seldom seen, rare....and a fortune if ever a set did 'surface' anywhere.
Then I saw my first Monoblock A's.....and they became my 'first love'. (Expensive yet again.)
My current Fox FX1's are about twice as strong as the Monblocks....but they're not genuine Smart.
Oh well....
Anyway...tyres....
205/45/17's will make your speed 72.36mph when your speedo shows 70mph..a 3.37% difference.
215/45/17's will make your speed 73.55mph when your speedo shows 70mph..a 5.07% difference.
Most speedo's over-read, viz show 70mph when you're doing 67mph, but with these your speedo
will under-read. The maximum difference factor ideally shouldn't exceed 2.5%.
(That then allows for the speedo error.)
For those interested, here is a link to a tyre size comparison checker...
http://www.alloywheels.com/Tyre_Calculator