Good clues guys, thanks.
I saw him again tonight, looked up CTS-V, bingo, it is a CTS-V wagon! No plates yet, I'm guessing 2011 so according to the web it puts out 556 HP, so I'm not feeling to bad tonight. And hey, I did get the jump on him...Lol!
I had something like that happen to me one night when I lived in Vegas. I was driving stop at a light and a Mercedes sedan pulls up next to me the guy ask whats your car got. I was driving my Fox at the time it had 347 afr heads bigger custom cam 350rwhp..... Anyways my buddy tell him its stock. Light turns green we take off I spin and we are neck and neck. I'm thinking as soon as I hook I'm gone. Not exactly what happen he pulls me I was like WTF 4 door Mercedes 4 bucket seats what the hell is in that. We get to the next light he waves smiles and turns off. I get home and look it up it was an AMG S55 it had 550 hp and a tone of tq that started off at like 2000 rpms. Oh its just a turbo v8. Sweet car if you have the money for them. The way my Mustang is getting built now that will never happen again though.