Also, something to possibly consider: reach out to customers and ask them how much they need IE6 support. Unless it's healthcare or government, I'm not sure why anyone would use IE6 by choice. Would deprecating support for IE6 lose every single one of those customers?
A big chunk of the old IE users were military people deployed in the Middle East. I'm of the understanding that they have/had some sort of Internet Cafe setup on base, and I guess they were running older browsers.
