I'm going to agree with Auto-X-ZTS on this. A big rear sway bar with soft springs is not a setup you want to run on a race track or a highway IMO. This setup is just begging to snap oversteer. What may work well for autocross may bite you on the track (or highway).
A 24mm is the largest RSB I would consider putting on a Focus and only with at least a 22mm front bar and stiffer springs.