X4 slot will give very good bandwidth with expensive card. [URL]   X1 cheap cards will not. [IMAGE]  
Hello My Dell T3500 has a 0XPDFK mother board with PCIe 2.0 sockets and I wish to fit a USB 3 card to it. I am undecided whether to purchase a card capable of 5Gbps or 10Gbps. I have a spare PCIe x4 socket suitable for a card but am unsure if I will get the full bandwidth benefit as my motherboard is PCIe 2.0 rather than the PCIe 3.0 that the cards seem to rated at. Will USB 3 run slower due to the age of my motherboard? Thank you Mark.
T3500 USB 3 upgrade