How much would a 17x8 or 16x8 be weight wise? Lighter wheels = less rotating mass which = better braking right?
...and better accellerating and better motion control, which translates to lighter springs and shock rates, which can keep tires in contact with the road better.
That is one of the problems of the plus size wheel craze is that they keep getting heavier and heavier, which is why they have to continue to hog out more and more material to try and keep weight down.
One of sports racer magazines did a wheel size comparison not too long ago on a BMW M3. All things being equal in tires and suspension, as the wheel size went up was so did lap times. Now you can tune around that, but like I said above, but your then stepping things up, which means more expense or your settling for less performance.