I would stick with the bilsteins. The monroes don't even come close to the ride quality of a bilstein strut. If you really don't want to spend the money on the bilsteins then I would at least consider the KYB Excel G's for an 06+ impala/monte carlo with the FE4 suspension.

http://www.grandprixforums.net/threa...-with-KYB-tech