For referrence, this is what a 1900 (the same size as the CTS-V) will do on a G8. It's a long read, but it made around 460 RWHP with a Borla catback and OEM airbox I think, in order to get a CARB exemption. I'm sure we'll be seeing CTS-Vs putting dow similar numbers, if not a little higher, and this was on a OEM L76 longblock with AFM, not an LS3...
http://www.g8board.com/forums/showthread.php?t=1337