I use both the XT (M785) trail pedals and the DX (M647) pedals for trail use, my thoughts are:
The feel and stability in terms of the contact area with the cages is very different. When I looked into it the Shimano website pairs their shoes with pedals, that’s not to say they wont work on others but some thought has gone into matching them.
For example the sole of shoes such as the M200, M163, M089 have long rectangular bars that run down either side of the cleat area which are designed to sit perfectly along the contact area on each side of the XT trail pedal.
On the other hand the M647 has a wider, flatter cage which tends to means shoes with a more conventional rubber tread seem to sit better on the cage and give a larger contact area, e.g. Rimes, Alpine XL’s, AM45’s, Tahoes, that sort of thing
Both combinations are good but with the right shoes the DX pedals are great for having the benefits of SPDs but with more sole contact.
HTH