I'll have to double check, but I've got a stock one off of a 2011 Automatic Mustang GT. I'm upgrading to the boss rear sway bar (non-laguna seca).
Well, as of right now, I've got some pretty soft lowering springs (Steeda Sports 175 in/lb) and "ok" dampers (Steeda Pro-Action), along with a watts link with my roll center set as low as possible. I was going to go all-out this fall on some nice, high end coil overs, but have decided to do heads/cams/intake instead.
So, with such a soft lowered suspension, the rear rolls a little too much for my setup, so I want an ever so slightly larger sway bar. And the Boss (non-laguna) sway bar is just slightly more stiff and is only 68$ through Tasca and should give me what I need. The other option is to go full adjustable, but when I do go with a good coil-over, I'll be yanking the sway bars. But that will have to wait until next year.