its about 5%
It all depends on what type of tyre you drive & how stiff the sidewalls are.
in other words I have currently 50 series fitted to my car on a 15\" rimm. They feel stiffer than the 45series tyres i had fitted before them on a 16\" rimm
However....lets just assume you would have the same tyre. You will need to pump up the 40 series more than the 45 series. The 40 series will be less forgiving than the 45 series. The 40 series will absorb less of the road bumps than the 45 series.
assuming you are putting a 205/40x17 on your NB8B. The 45 series would also be a fair bit taller. which means your accelertion would also be slightly less.
handling....on a flat & smooth piece of road....the 40 series will always win. Just don't hit too many bumps.
I have a feeling the 45 series would be just a little too tall on the 17\" rimms anyway. But don't quote me on that.