I bought an '06 red/white stripe (fastest color : ) 4 option car new, still have it, and love it. All of the preceding info is good, talk to Shelby if your serious on a car- he's a wealth of facts about the cars and usually has good inventory. Ford GT Forums for owner input.
However, there is one thing that has been missed so far. Air bags.
Takata air bags.
I, and lot of other owners have restricted the driving on them until Ford has replacement bags, sometime on 2017. I don't like driving a car with a loaded shotgun pointed at my face. You can't disengage the driver bag. The older the bag gets, the more volatile it is.
If you get a car in the next year, make sure you get the airbag status from existing owner or dealer.
The up side is get to drive my 289 Slab more
