HP Z820. Got one. Love it.
I went with ADK as well. Eric and I discussed every little aspect of the build and I am quite happy with mine. It came out better than if I had tried to do it myself.
I'd be happy to discuss your needs and put together some competitive pricing for you. Here is a link for a system comparison Dave Helmly did, and it includes one of our Tsunami CS6 editing workstations in the review - http://blog.sharbor.com/blog/2012/12/adobes-dave-helmly-discusses-thunderbolt-for-pc-and-t sunami-riptide/
Safe Harbor Computers