Both are TR4 motherboards, but the only noticeable difference is one has 2 PCI-E X1 slots
Can anyone please help me make noteworthy differences for which one to buy?
I would go MSI. Not much difference though.
If its of any help, tweaktown has comprehensive reviews of both, well worth a read if you have these two as your options:
https://www.tweaktown.com/reviews/8508/msi-x399-gaming-pro-carbon-ac-amd-motherboard-review/index.html (says gaming pro carbon, but is the SLI plus you linked)