To each their own. We all have our 'thing' or 'things' that either attract us to a car, or push us away. One of MY big ones is weight. That was the overriding factor for getting my current driver instead of a new (at the time) 2011 GT (or waiting a short while for a 2012 Boss). There were other things, but that ended up being the deciding factor. When the word on the street was that the 2015 Mustang would lose weight, as much as a couple hundred pounds, that got me excited, hopeful, and seriously considering jumping BACK to Ford. Gaining 100 lbs....what a disappointment. Ya, more HP might make it faster. Yes, GM proved you can make a bloated pig handle (see Camaro). But a bloated pig is a bloated pig, and now that includes the Mustang GT (and not just the GT500). Maybe the next generation Mustang...
/admitted weight nazi rant
Look in your manual to see what they list your car's weight as. Since this is supposed to be from a manual the ratings should be determined the same way for both.