External cable size is limited by flexibility. In theory the 4x variant could drive an external GPU at PCIe 5 x16 bandwidth. Alternatively, it could drive a 4x

External cable size is limited by flexibility. In theory the 4x variant could drive an external GPU at PCIe 5 x16 bandwidth. Alternatively, it could drive a 4x16 card and have bandwidth left for fast SSDs and fast Ethernet and various USB stuff at the same time. That sounds great for laptop docks.