I originally ordered the Performance package, but I updated my order to remove it. I too wish there was more detailed description of what is actually included vs not.
The primary reason I made my change is I think the 20" wheels will kill range significantly. The 310 mile range is definitely only possible for the Aeros on 18". The range on 20" wheels might be as much as 15% less given the larger wheels and lack of Aero covers. That would bring range down to 263.5 miles. That's a pretty significant difference and could be the difference between needing a supercharger stop or not.
I also think the 18" wheels have a good chance at being faster overall, since they have less mass and will give the car lower final drive ratio. 155 vs 145 mph top speed is completely irrelevant since I will never drive the car that fast. And for those that try, I would expect it to take a very long stretch of road and that it will not be able to maintain that speed for very long anyways.
Take a look at C&D tests here:
Effects of Upsized Wheels and Tires Tested