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, 6MT, Le Mans blue - Quaife LSD, JRZ RS Pro, JRZ camber plates, Eibach ERS, full M3 susp, custom toe arms, Powergrid end-links, SS brake lines, brake ducting, Michelin PSS, UUC SSK, ETS FMIC, ER CP, Perf. Exhaust, VAC RSIK, Sparcos; work by VAC Motorsports in Philadelphia