It's a bit tedious, but at least you'll know where all of your memory is going. You should be able to drop down Chrome into multiple processes, then determine which process is tied to which extension or tab. To determine exactly where your RAM is going, you can open up task manager on Windows (Ctrl + Alt + Del) or utility monitor on Mac (search 'utility monitor' in the Finder).
Remember, Chrome isn't just one entity: it's a collection of tabs and extensions, and each one takes up a different amount of RAM.