Whats the best torsion bar size to increase handling????

Question:on a 70 Dart what would be the advantages of having torsion bars bigger than original 340 bars. I have completely rebuilt the entire front end(orig. KH discs and factory sway bar) added good shocks all around, rear sway bar and want to upgrade the t bars. Frame connectors are in the works. I have changed directions on the building of the car from hot street to a dependable cruiser that handles very well. The motor is a 360 Magnum which should weigh very close to a 340. Would this be a case where bigger(bigger than 340 bars) is not always better?? Any advice would be greatly appreciated. Thank you.