Why? The cobra is just another trim for the mustang.
Kind of like the cavalier. The 4 popper version is called a cavalier, and the V8 version is called a GTO.
The cobra is a Mustang that is sent to SVT to do. Ford itself will not "make" cobras. If you want to compare cobras to something along the lines of a GM car, think of the Firehawk or SS Camaro since those are modified by SLP.
There are no SLP designed GTOs. So take a GTO VS Mustang GT. The GTO will hold its resale and will mop the floor with a Mustang. The only Mustang that will hold its own against a GTO that isnt a Cobra is a Mach 1.