are either of these better than the stock 4 link the mustang has? Im thinking a nice 5 link would give better traction and less drifting in turns. Correct?
The number of links doesn't really tell you a whole lot about the configuration. The biggest problem with the stock configuration is that the upper links are angled - in order to provide lateral location and to control the torque reaction of the axle. Consequently, they don't really do a great job at either role, and that geometry actually 'binds' as the suspension goes through a lot of travel.
The set up most folks seem to rave about has two lower control arms that locate the axle longitudinally; a single longer torque arm that manages the torque reactions of the rear end; coil-over-shock for spring and damping, and a Panhard rod to locate the axle laterally. Companies like M&M offer a set up like that. Not cheap, but those who use it seem to like it.
Probably the ideal way to locate the solid axle would be a twin parallel upper and lower control arms - both adjustable, and a Watts-link for lateral location; coil-overs for spring/shock. But it would take a LOT of fabrication to create a set up like that for the car.