Likewise, I tried to return a version 302 board for a version 400 board. Spoke with Intel Customer services. The long and short of it was that the version 400 board does NOT exist. Despite what was written in the Product Change Notification, customer services told me that Intel never got around to producing a version 400 board. They offered me a GZ77GA-70K board instead, which I declined. I would rather keep my Thunderbolt-enabled board and work around any USB3.0 issues by installing a USB3.0 PCI-E card, instead.
If this information is not accurate, can someone pipe up and say that they do actually have a version 400 board?