i think you are confused. a rear strut brace is useless in ALL protege sedans, including the MP3 and Mazdaspeed, due to the design of the chassis. in theory, a rear strut brace ties the rear strut tower together to limit body flex at those points. in the protege sedan, the rear parcel tray, and all the bracing underneath it, ties the rear strut towers together. thus, you could say that the protege already has an integrated rear strut tower bar. therefore, my original comment holds in that a rear strut tower bar is usless in all protege SEDANS. (the protege5 is a different case)
oh yeah, and body roll is not controlled by braces, but rather springs and anti-sway bars. and skidpad testing will show nothing as the mazdaspeed, MP3, and all trim levels of the protege have different suspension set-ups. also, stiff anti-sway bars and stiff struts and bracing will give better response in transitions, which are not reflected in skidpad testing.