What is the difference between ....

HIPER 409 CAT BACK SYSTEM & SILENT HI-POWER CAT BACK SYSTEM.

http://www.sumopower.com/hksexh.htm <---- found on this site and im assuming my car is a GC8 as the VIN number starts with that and its a STI V5 (can someone let me know if im right on that)

I assume that one is quieter but im wondering how quiet and does is sap power over the over? I had a HKS zorst on my old bugeye but I cant remember which one it was apart from it wasnt that loud in comparison to my Ninja i have on my classic now.

Both cars have full decats and the HKS was a lot quieter from what i remember and i know that it had a long silencer in the middle and some weird torpedo thing attached to the top of the back box?!?

Any help appreciated!