I don't play E6 so I don't know about particular restrictions, but I do have a pretty badass ECL 6 grapplemancer. It uses 2 flaws, but you could do it with just one, and it has a +40 grapple check at 6th level and does loads of damage. The items could be amped up to make it even better (it's an NPC so has lower wealth).
However, it does not use a garrotte. Are you interested?