As someone who has had an Atmos setup in my theater for about 18 months I can say this... Go 7.1.4. You will be lacking the full experience with only 2 overheads.
Heck, I would recommend 5.1.4 over 7.1.2 as well.
Don't get me started on non-direct radiating (monopole) surround speakers though...
I traded in 4 QS8s and got 4 M3s for surround duty too, but again, don't get me started. LOL
Get 4 M3 speakers overhead, drop down your surrounds like you mentioned, and give it a whirl.