The performance down side to a Radius setup is the twisting of the axle, which you can fix by eliminating one upper axle mount and then the lack of any kind of adjustable anti squat. As well as a caster angle that changes rapidley under flex. On the plus side, the U-Joint angle stays very consistent.
As for soaking up bumps better at speed, I dont believe it, that sounds like someone had a setup that worked really well because of shocks and good bump stops, or maybe it was a fitment issue with the upper link that forced them to go with it. You have to remember the links aren't soaking up the bumps, its the springs, shocks, bumps and tires that soak it up, the links just keep the tire and axle in place. Or perhaps the vehicle did better because it was a radius arm system with large bushings like the Ford style that helped isolate vibrations.
