Here's the link for the plugs that most are replacing with. These are suppose to be an upgrade from what we already have. The IK20 is standard and the IK16 is one range colder. Don't forget that we use 12 plugs in our V6's. Hope this helps.
If you do decide to change your plugs now, you might want to consider changing to the Magnacore plug wires also.

http://www.sparkplugs.com/results_cross.asp?pid=5303
http://www.alamomotorsports.com/Magn..._mercedes.html