help me looking for a high flow cat only

Magnoflow cats are what most catted midpipes come with, so I'd go with them.
As far as which one...eeesh...they've got a ton of em. I just went out to their site and tried to do a little shopping for ya, but there are just too many! You'll want the 2.5" of course, but maybe someone else can jump in with some details. Otherwise, you might want to call them.
www.magnaflow.com