i had the same questions, and the forum was a lot of help. here's my thread:
http://www.camaro5.com/forums/showthread.php?t=124966
the general consensus is that 1 7/8" headers are best. if you want to go over 500 horsepower, then probably go with 2" headers. i'm not sure how a cam will come into play with all that.
also, getting them ceramic coated is a good idea