I ran mine with the Schum kit yesterday on a rather bumpy hard packed clay track.
I first tried the kit layout (front shocks), then shocks at the rear with drilled arms and finally the Schumacher kit.
I felt little difference between the kit layout and the drilled arms rear shock mod. The rear shocks felt a little grippier but nothing major.
As usual, the CAT drove like it always does on slippery or bumpy tracks as a really pronounced "front end car", with the rear drivetrain sometimes a little "lost" in the proces (if you know what i mean).
Mounting the Schum kit and swapping the rear arms made one hell of a difference. Suddenly the rear end felt rock solid. It generated so much more grip, i had to change a lot on my setup to get enough front end bite to compensate.
Is it better ? I don't think it's actullay much faster on a single lap, but it certainly makes the car a lot safer/easier to push hard on bumpy, slippery surfaces and that's always a good thing.