Backhalving?
Having run a CalTrac set up on my Duster w/minitubs I am very familiar with what they will do and won't do. It all depends on the track. At a good track 9's are reasonable. At a marginal track, 10's are borderline. With a 15/33 tire and a fourlink I can hook in the dirt.
My buddy went from CalTracs to a ladder bar and picked up 7 tenths, and the car ended being heavier after the ladder bar/backhalf installation. There's way more suspension movement before the car moves with leafsprings, regardless of the type of traction system used.