Another problem with larger torsion bars is that the chassis may not be able to handle the larger bars. Essentially the unibody becomes a spring. If subframe connectors, torque boxes, etc have been added, larger bars become more effective.
I think this statement is the most over looked issue when upgrading to a larger torsion bar. With a STIFF chassis, you can run larger bars and not effect the ride. I run 1.02" bars in my 6.1 Hemi Duster with the complete US Car Tool Level 2 Chassis Stiffening Kit and it's not stiff riding, but it sure doesn't lean into corners!
Actually that is incorrect "common sense" thinking.
No chassis is perfectly stiff, every chassis has spring, and factors into the final equation. A stiff(er) chassis is always preferred, as it narrows down the items that are tunable by choice and with ease.
A stiffer chassis likely needs a softer TB for equal handling characteristics, applications, same concept applies to higher tire pressures or lower profile tires.
A stiffer chassis with stiffer TB's will move the performance envelope higher, if tires, brakes, engine and driver can achieve it.