2008 Grand Prix GXP

I'm in the process of buying a 2008 Grand Prix GXP. I've done a bit of research and find the front rotors are 12.7" and the rear 12", both cross drilled. What I can't find out is whether the front calipers are single or double piston. I'd also like to know whether fitting F Body aluminum double piston calipers is possible or makes sense and whether the only benefit is the reduced unsprung weight?
Keith