IMHO, If this is a American Raceway type/style track. Then it would *not* be similar to the Super Speedway/Punchbowl Blue King type tracks where Vipers, FoxTail's and Supro's rule.
If this is true then you *will* want a higher downforce body. As Trevor said, you will give a little down the chutes but be much much better in the gutter turns.
I'd start thinking in the direction of these listed in order of approximate level of downforce.
Because you mentioned G12, I would recommend trying .005 thick bodies as you are not generating enough top speed as G27/G7 cars to be as concerned with body collapse issues.
I usually do lower weight 4x5 wing kits for G12 and then add stiffening tape/body armor as needed. My theory is it is easier to add stiffening than it is to try to take some excess weight away.
Your initial goal is to make the body under 8.5 grams race ready. With a little experience under 7.7 grams. When you get really good you can occasionally build them under 7 grams. I'm giving these weights to start you thinking about all of the individual components needed to get to race ready up to and including paint.
Or if you can afford it, Buy a premount from one of the pro's like Trevor, Brad, Beuf or P.A. Watson as a reference. Just make sure they know the track type, builder and banking specs and condition before you buy so they can assist you with choices. I have huge piles of failed experiments before I started to get competitive enough, to know positively, you would be well advised to learn a baseline from them instead.
Hope this helps