I agree with ChurchX
To me that is optimal. Lighter weight is king not just for better 0-70 times, or carving , but also better for MPG get up and go.
That video on pg. 1 was informative. Even if you go 18" , on a good forged wheel, anything quality will weight 16-18 lbs. On a 16x7, you can get weight down to 10.5- 11.2 lbs (SSR Type-C or Volt TE-37) , or even a good forged 17x7 , weight will be about 13.5- 14lbs for something upper level.
Going 18" or 19" is more of a bling bling thing. The car was designed around a 17" wheel, plain and simple. A 16" wheel could be good in that it's lighter, but needs to set up right so you have a similar diameter as the stock wheel (so maybe a 215/ 50/ 16 tire size (have to check the comparison wheel conversion calculators that are online ) :
http://www.1010tires.com/Tools/Tire-Size-Calculator