I thought you might find this interesting, there is a great EPA website that keeps track of mileage estimates for different cars.
EPA Website
Check out the city/highway mileage estimates and hp for the base Boxster with manual trans.
2000 19/27 217 hp
2003 20/29 228 hp
2005 20/29 240 hp
2007 23/32 245 hp
Interesting, I want 32 mpg with 245 hp, thank you very much.....
Ed