Sorry it's long.
What springs you run front and rear will make a difference what diameter bar works best, if at all.
In saying that, objective of running the car in autox's, with the suspension setup I'm running, testing both the SS and base model bars, the base model Cobalt bar (18mm) works better for me with just one person in the car than the SS (24mm) bar.
(I thought there's a 19mm bar on certain rear Cobalts. I could be wrong about that, but I'd like to try it if I find one.)
Two people in the car with the base model bar and it's too soft. Chassis roll increases quite a bit, unweighting the inside rear tire.
Two people in the car with the SS bar (24mm) and it felt just a tad too stiff. But it is very drivable, helping the car rotate and can easily be balanced with the throttle all through a corner. Less chassis roll.
One person in the car the bar is too stiff. Although it did make my non-LSD transaxle act like it had an LSD.
There's a lot of variables at play and stuff I'm leaving out. Driving styles/preference, suspension setup and usage is something else to consider.
The swaybars are cheap. Test them both out to see what is comfortable for you and do it safe manner.
Autox is great way to do that safely and it's fun. It can also closely simulate what you might ask of the car to avoid an accident on the street. You dont want to be surprised by unexpected handling characteristics getting you into an accident while trying to avoid one.
Typical autox courses are wide open areas that if loss of control happens, the only thing to hit is cones and flat spot tires.
You won't be able to change out the bar between autox runs but you can disconnect one endlink to easily try with and without the bar.
