I recently put on the Eibach 25mm rear sway bar and I still have the OEM stock sway bar on due to problems with fitment. Since I've had it on I had a nice warm day to see what I got. With everything out of the rear and tires down to 32psi I noticed it was a bit tail happy if pushed a little more. It honestly scared me. With the stock sway bar in front I don't feel as confident as I did with the OEM bar. So, if your going to keep the front sway bar stock I wouldn't go with anything bigger than a 24mm bar in the rear. I do think however the Eibach kit will handle very well once I received the right bar and have it installed. With the 16X7 rotas and 215/45/16 kuhmo xs my car should be a delightful drive.
-Zetec Crew #215
Volant Intake, SVT Snorkle, By past A/C, AFX UDP, Copper Plugs, 9mm Plug Wires, Toms Tune, Roush springs/shocks/struts, Eibach Sway-Bars, C-F-M Racing Lower Engine Mount.