5D2 -> 5D3
rebel -> either 5D2, 6D, 7D/2
7D -> either 5D3 or 7D/2
Depending on your purpose these might change. A 5D2 to 6D seems not a very big upgrade. However if you're in a business and 5D2 is enough for most of the things you do and it's already near breaking point, an upgrade to 6D isn't unimaginable. Let your purpose/goal decide what's truly an upgrade for you and not just because whatever has better specs.