hi crencom,

Don't know which motherboard fits best to you, but I'd prefer the Gigabyte one. I've had two Gigabyte products in my old Computer and, contrary to an old Asus board, never got problems with them.
imo SLI isn't that important at all on OSX, because there aren't so much GPU-heavy apps (expecting X-Plane on highest details where my MBP sounds like the Ingame-Airplanes)

greetings