Just to let you know, so that you won't be spending for features that suddenly you cannot use/achieve:
Your Gigabyte X99 SLI will only run the M.2 PCIe3.0 x4 SSD in x2-speeds (not x4) as the M.2 socket shares bandwidth with other lanes/slots of that particular mobo. Also, if you populate the M.2 socket, two of your SATA ports will be disabled (consult your manual which SATA ports these are to avoid disabling any HDDs/SSDs connected on those ports).
The Gigabyte X99P SLI is the board that supports M.2 PCIe3.0 x4 SSD in x4-speeds.
I am not sure which one of the Gigabyte boards you have, the X99 SLI or the X99P SLI.