If you want to see real data, check out Fuelly:
Browse All Nissan 370Zs | Fuelly
Its a website where you can key in your fill ups and it runs the stats for you. The cool thing is though, you can browse all of the cars and motorcycles on the site.
Mine doesn't show up yet in the general list because I only have two fillups in the Z thus far:
http://www.fuelly.com/driver/lesspeoplemorerobots