im no scientist but Ive reported this on the same stretch of freeway:
2010 LGT Stock:
Cruise control @ 65 mph for 10 miles = 32mpg
2010 LGT with my Q300 added on:
Cruise control @ 65 mph for 10 miles =36 mpg
Unfortunatly for the city its now a solid 18.7 down from 20ish
But this is most likely due to my new leadfoot habit and my desire to hear some nice boxer rumble and see the numbers fly...haha!