My understanding was that the red panel was in a sense, just a novelty feature ... you know, to get you to want to have the "special" edition. Though I do not think the workings of it were any difference.
When I purchased the 6600, I could have go the 7700. Later I wished that I had got it, when I knew more about the differences. However, if I were buying today, I would skip over both, and go for the 8200 or 8900. Both newer machines, but with a lot of improved updates to the 6600/7700s.