Well, thanks for your reply RogerB.

I also think that the 17" is as far as you can logically go for the CSVT (it is after all a sport SEDAN), with the 215/45/17 size tires for the CSVT.
But if you want to put tires wider than 215 mm on these rims, you have to go with the 245/40/17 tires!! I guess they won't fit on the CSVT.
So, I would be stuck with the 215 wide tires.
I would prefer the larger 225 tires on the 16" rims which gives me more rubber on the road as you say.