Is the advantage to getting the watts six bar linkage over our panhard bar type rear suspension just the lateral movement in the rear suspension during travel?

 

Yes, the laterial movement all but goes away with a watts link.
The roll center can also be easily adjusted on some of the newer designs.
But you would almost need to be Xcrossing for prize money to actually
benifit from one. Its OK for normal street use but its not a commonly
installed modification around here.

The OEM panhard bar is at a 4 degree angle to the axle at rest and
almost 44" long. With 4"s of suspension travel, the laterial movement
is not noticable.
Do the math/Trig and just see how little the sideways movement actually
is with the OEM Panhard Bar set-up.

 

Agreed. Post in handling section and see what input they have but IMO not neccessary for street/DD.

 

It's not necessary, but I've read a few posts of people that have had them installed on their street cars and say that it is a night and day difference. I plan on putting one on eventually, but there are definitely other suspension mods that will be a bigger improvement in the overall handling that I would do first. Honestly, a lot of guys comment on how much more planted the rear of the car feels after they switch to an aftermarket panhard bar, so unless you just really want to spend $700+, that might be the better route to go. The change from the factory rubber bushings to polyurethane coupled with the stiffer bar you get when going aftermarket will yield a noticeable improvement.

 

I replaced the soft OEM rubber Panhard end bushings with
some nice Polyurethane units from Prothane.

055-102 $21.95 Prothane Bushings - Rear Tacking Arm

Best $22 bucks I ever spent.
The difference is like night and day.