First let me say that I can understand why you payed $5k over, because you wanted the car then and there & you didn't want to search or wait a little bit to find a dealer who's not bending the customer over and you didn't care about throwing away $5k of your earned money because you wanted that car bad enough and you had the money to do it.
To pay $1k over MSRP for a standard Mustang GT that others are selling for regular price? That's stupid, to pay $1k more when it's the Shelby GT500 which is with respect to a car that is special and will always stand out from the rest & one day hold a collectors value when most dealers are marking them up $5k or $10k maybe not so crazy. A Camaro SS fit's into the Mustang GT rank not GT500. A 5th gen Z28/ZL1 that was built either by a company like SLP or GM fit's into that rank with the GT500 but not the SS.