Other than the FD 55mm, I'm struggling to think of any "recent" use of the 55mm focal length in anything but an EF-S lens.
This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.
Having actually done this test (7D v 5D2, 24" landscape prints) I can tell you that nobody can tell the difference or tell which print comes from which at low to mid ISO. Out of camera there are some small differences between the two at low ISO, but those differences do not survive post work or printing. I've even challenged people with 100% unlabeled crops, after post processing, only to have them completely fail to say which came from where.
Both make excellent 24" landscape prints, and very good 30" prints, and that's about the limit for critically reviewed landscape prints (i.e. close viewing; judging on fine detail). I highly doubt the 1Dx will change this for landscapes since the limiting factor here is the resolution of fine detail like distant foliage.