04+ are 6.5"/6.75"
We have this weird plastic speaker baffle thing for our doors. However, not all speakers that are classified as 6.5" ARE actually that measurement or utilize the same spacing for mounting holes. Few speakers will screw in exactly in the same spot as the OEM speakers. You make them fit
Here's what they look like for everybody else...
2004 Pontiac Grand Prix door speaker - eBay (item 230484113791 end time Apr-01-11 13:10:25 PDT)