So I've run into this on several websites. This is ignoring the "sport" brakes. Other sites don't have this issue. Is there something I'm missing?

I put in 2008 G35X for a car and get two different rotors:

 

Sounds like whatever site you're using has its parts mixed up.

330 mm = 13" = sport rear
(12.1" = non sport rear)

320 mm = 12.6" = non-sport front
(14" = sport front)

 

the best thing would be to call the shop/site you are trying to buy from but on R1concepts they only seem to have one size listed for 08 G35X. They have an instant online chat and know a lot, ask them to confirm and save the chat in case you need it if they are wrong. Or the better thing is to contact them through email in which case their supervisor Dee will answer with a definite answer.

 

Those are both front rotor parts I posted. I also had this same problem at the local NAPA store (and Napa online) as well as other online web sites.