Introductions & Greetings - LS1 Convertion Question

I have an LS1 02' Camaro Z28 that my Dad and I are re-building the engine for. I am contimplating putting LS6 heads and a LS6 cam but I'm worried about gas mileage. Can anyone tell me if it would drastically drop my gas mileage or not?? I want the extra horsepower but not if my gas mileage is going to drop significantly.

Not the best place to post this go to the genIII section and repost. Might even be a sticky that might help you out there.