Dedicated workstation generally go with the X99 platform.
Workstations generally involve multi-threaded apps and for a combination workstation / gaming platform, you'd want Z97 over H97
https://www.pugetsystems.com/labs/articles/Z97-vs-H97---What-is-the-Difference-562/
https://www.pugetsystems.com/labs/articles/What-is-new-in-Z97-and-H97-561/
mATX is just "smaller" than ATX and with that reduced size comes compromises on what features can be added, how robust the MoBo can be designed, and increased costs ... if in a mATX case, cooling of system components is also impacted.