Neat, thanks!
I personally run 24/17 on my RS and RSTi. I don't have any understeer to report, likely due to having good front LSDs in both.
I had a 20mm on the rear of the RSTi for a while, but it broke the swaybar mounts off my adjustable lateral links at an autoX, so I ran the next few years with no rear sway at all.
No rear sway had amazing cornering grip, but was prone to skip a little depending on surface. I could stay WOT through most turns w/o the rear end stepping out.
I finally swapped to new lateral links this year (Whiteline) and put the 17mm back on for now and that's enough that I can step the rear out whenever I need to for additional rotation.
-- Dave