here ya go:
http://www.a5oc.com/forums/
there are a LOT of topics on this subject here. Honestly, from what I have been reading, there is a difference of about 5 mpg hwy between the A5 and S5. Then about 3-4 mpg difference in city driving. I guess it depends on how aggressive you drive. I am leaning more toward S5 myself. The auto trans cars seem to do BETTER than the manual trans, but I go manual trans in cars. For a truck, esp if you are pulling something, I would get an auto
Differences between the 2 are: the sports seats, type of leather (i can't tell really from pictures), rear bumper and front bumper/grille treatment. Even the A5 S-line is different than the S5, but not by much.
It all depends

Most ppl say BMW 335xi over A5, and S5 over them both. Also, insurance for the S5 is 22 bucks more a month than the A5, annual gas is about 200 bucks more for the S5 than A5. To me, I can justify the extra cost
