I have M60 fronts, VP180 center, and M3s for the 4 surrounds and 4 overheads. It works out really well.
For a 5.1.4 setup, I would put the 3 up front like normal, and the 2 surrounds should be to your sides slightly behind the listeners' heads.
The reasons for this are: 1) in a 5.1 setup, the surrounds are side surrounds, not rears, 2) if you place them directly to the sides of the listening areas, someone's head will block that side surround. By putting slightly behind, then there are no heads blocking the sound. Dispersion from the speakers should cover the listening area just fine.
Then just make a "box" around your listening area and put the overheads in those positions. In an Atmos 5.1.4 setup, the rear overheads can be slightly further back from the couch than the fronts are in front of the couch as you have almost no sound energy coming from back there.
If you want an Atmos/DTS:X setup (and why not, right?) Then you want to push the front overheads and rear overheads out a little more than Dolby spec. There IS an overlap between the Atmos and DTS:X spec, and you want to put them into that space. This holds true for 5.1.4 and 7.1.4
For a 7.1.4 setup, then I highly recommend putting the side surrounds slightly in front of the listening area. By slightly, we are talking 6-18 inches. Then the rears should go on the back wall, not in the corners, but more inline with the front L/R speakers. The reason for the side surrounds being slightly in front of the listening area are the same as above with not having one person's head blocking sound, but since you also have dedicated rear speakers, and rear overheads, putting the side surround forward just a touch helps to fill in the "gap" that exists between the front left/right speaker and the side surrounds. In many rooms, this gap is pretty big. That is why a lot of people liked the option of using front wide speakers when that because available years ago. It won't mess anything up, and works out very well even without Atmos/DTS:X content playing. There have been tons of real world tests and experiments on AVS about putting side surrounds forward of the listening space well before immersive audio even existed and the consensus is that it is a better/smoother soundfield.
