Can you confirm if this is the same official site of your motherboard you have mentioned: https://www.gigabyte.com/Motherboard/GA-Z97X-Gaming-3-rev-10#ov
It states that the M.2 socket of the Gigabyte GA-Z97X Gaming 3 are:
"M.2 for SSDs drives with up to 10 Gb/s data transfer
"GIGABYTE G1™ Gaming motherboards come equipped with an onboard M.2 slot, providing users PCI-Express connectivity for SSD devices. Delivering up to 10 Gb/s data transfer speeds, M.2 offers users considerably faster storage performance than current mSATA and even SATA Revision 3 (6Gb/s) storage devices.
Based on the specs, your motherboard doesn't seem to provide PCIe3.0 x4 speeds on its M.2 socket, only 10 Gb/s (equal to 1.25GB/s), which is roughly PCIe2.0 x2 speeds.