Slim filters are really slim?
CP's are usually thicker since they have two elements (one rotating) and outer threads for a lens cap. The slim versions are 5mm including the outer threads.
I believe certain Hoyas may be slimmer since they don't provide outer threads for caps..........but their quality isn't as good as Marumi or B+W.
If you are in the US there is a reputable dealer who can answer your questions by calling their 800 number. http://www.2filter.com/marumi/marumicirpolarizers.html