Mixing 2.0 and 3.0 versions of USB, SATA, and PCIe

[Aegean BM]

My wireless router does BGN. Suppose it has 2 N clients using it. As soon as a G client joins, everyone is downgraded to G. A USB 2.0 device plugged into USB 3.0 connection will run at 2.0. Will it also downgrade OTHER USB 3.0 devices? Same question with SATA and PCIe.

It's not just theoretical. I'm upgrading my mobo, memory and CPU.
Will my PCIe 2.0 sound card downgrade my PCIe 3.0 graphics?
Will my USB 2.0 keyboard and mouse downgrade my USB 3.0 wireless N?
Will my SATA II HD downgrade my SATA III SSD?
Is this why motherboards usually come with dual standards?

 

[das_stig]

You can mix and match USB2/3 device without worrying about speed drops, but I normally connect USB3 to the USB ports supplied by the motherboard chipset and USB2 to any third party chip as these are not as efficient.

PCIE-3 lanes run independently.

SATA device run independently.

 

[Aegean BM]

You can mix and match USB2/3 device without worrying about speed drops, but I normally connect USB3 to the USB ports supplied by the motherboard chipset and USB2 to any third party chip as these are not as efficient.

PCIE-3 lanes run independently.

SATA device run independently.

Perfect. Much thanks. I had a simple question, but Googling kept telling me only about backwards compatibility that I already knew.

 

[Aegean BM]

Best answer selected by Aegean BM.