I have sway-a-way 1.14" bars in my Duster (avatar pic). It is intended primarily for track use. The ride is firm but not really any firmer than your typical late-model import sedan. At that stiffness though you need some wide grippy front tires to take advantage of it or it'll just understeer all over the place. I previously had 1.00" bars which were too soft once I upgraded to the current wheel/tire combo, it would hit the bump stops in really hard cornering. But once I put the 1.14" bars in I had to dial in more camber (went from basically zero to -2.0°) to keep it from under steering. It has a pretty nice neutral feel in the corners now. Car also has Hellwig front and rear sway bars with the rear being adjustable and it's on the stiffest setting, also running Hotchkis leaves in the rear. It handles really nicely except in quick back-and-forth stuff (slalom) because the shocks are just stock replacement junk and have way too low of a damping rate to control the wheels.
So in summary, from my experience 1.08" or bigger will work fine but to get the most out of them you need good shocks and wide grippy tires. And stiffened up rear suspension so it doesn't understeer like crazy.
