Unless you have an LSD as noted, don't do the rear sway. You will be worse off in turns. The inside wheel gets nearly all of the power in a tight turn because of that open differential; a thicker rear sway will actually lessen the grip and you'll have even less 'push' going through.
FYI rear sway = drop the subframe, which is very expensive. Do it at the same time as LSD + subframe brushings.
2011 BMW E92 335i - Le Mans Blue/Black, 6MT, M Sport package