40 gbps(This mean 40 gigabit per second) = 5 gigabytes per second. Pci-e 3.0 supports 3940MB/s. article don't say but this card need usb 2.0 and asus specific ThunderboltEX 4 header. This way card easily achive 5gb/s = 40gbps
Bit and Bytes are different
usb 2.0 is needed because 3.0 4x slot...