Did the '07 GT500 come with the HIDs? Or was that just '08 and up?
HIDs weren't available on the '07s. That was a new option for '08 Mustangs, including the GT500. The only '08 Mustang that came with HIDs standard was the GT500KR (except on KRs built for Canada, for some reason).
The nav system option was added in late '07. It is in the '08 Mustang brochure but not the '07 brochure. The nav system and Shaker 1000 audio system were mutually exclusive options - you could not get both together.
Vapor silver metallic and black stripes were new to the GT500 for '08, although Green Bay Packer Ahman Green was apparently able to get his '07 GT500 in that color combination.
I had been staying out of this thread because it looked like you were interested primarily in engine details, and Osiris already gave you the correct information on the difference in balancers (I would have posted this had he not alreasdy done so).
2013 Boss 302 gotta-have-it green
2008 Shelby GT500 torch red with black stripes + sequentials
2001 Cobra mineral grey with 2003 Mach 1 shaker hood
1996 Cobra color-shifting mystic paint + sequentials