v6's are about 100 lbs lighter than the 5.0s and almost all of it is b/c of the lighter engine / engine block. I believe there are few other parts missing or lighter weight on the V6.
I've got about the fattest Mustang of them all. That's FATTEST.... unfortunately not FASTest.
GT Premium Convertible Automatic... think I'm about 3,730 lbs+
It has extra reforcing crap on the bottom that the coupes don't have. Like the front LCA front brace... and some rear body bracing, etc.
It was the the pimped out showroom model with pretty much every single option available, except for heated seats.