Congrats on the new ride, IMO the there is very little difference between all the intakes for these cars. I am sure some will say different, but your only looking at a few RWHP either way. Just pick the one that you think will look the best under the hood. I personally picked the Volant after looking at all the same ones as you. The Volant looks cool, and DRCustoms will be getting a Superchips tune for it really soon, so your gains will be all that much better.
Happy Shopping, and enjoy that M6 GXP!!
G8 GT Panther Black, Sport/Premium Package
Superchips 91 Volant Tune, Volant CAI, Borla Cat Back
Home Link in Visor, Kicker Audio All around.