Below we see a 32Gbps-NGFF.M2 and a 32Gbps-TB3 eGPU implementation.  The NGFF.M2 interface directly attaches the video card to the southbridge giving better performance at the cost of inconvenient under keyboard access.  The Thunderbolt controller adding dragging latency  but provided a convenient single cable solution using the external TB3 port.   Notebook 17"  Clevo P870DM-G Intel Z170 chipset with 8Gbps (Gen3) Southbridge PCIe ports i7-6700K CPU 64GB RAM 512GB