I drove the S5 on the Homestead Miami Raceway (1/2 oval + in-field). The S5's Interior is 1st class and exterior design looks great as as well. On the track... it felt a little weighed on tight turns (it is a longer/roomier car afterall. The V8 is silky smooth to redline and had no problem getting up to speed. The car stops well with its bigger brakes.
Personally, I don't think any of us can get anywhere close to the performance limits of the S5 (or other similar cars mentioned above) on the streets - not legally anyways. IMO, the S5 is a great GT car for the following reasons: 1) travels effortlessly from point A to B, regardless if it's on the freeway or HWY1, 2) brings great presence without drawing unnecessary attention, and 3) rewards the driver with fun driving experience and passenger with refinements and amenities. If that's what you are looking for, you can't go wrong with the S5.
Just my 2 cents.
