M-ATX and ATX

Solution
A good m-ATX motherboard will have pretty much the same features as a good no-frills ATX motherboard, the main difference being three fewer expansion slots.
They generally perform the same, and may have equal features such as high end sound and overclock capabilities.

If you are into ln2 cooling and record overclocking, perhaps not.

You can even get a M-ATX case that supports sli.
Asus maximus VIII gene, for example.