Just got off the phone with Calumet (UK).
I ordered the 5D3 on the day of announcement and in order to secure it I needed to put £100 down so I went and paid the full amount over the phone. In conversation the release date they have there is March the 22nd, which is a Thursday. Further there may be a possible deliberate association with it being 22mp on the 22nd.
If this is true then that's great, I've two weddings that weekend and can really put it through the mill.
1Dx is still labelled end of April though.