For time/cost saving reasons, I want to use a USB 3 cable as a USB 2 cable. The cable will be carrying other (slow) signals, and so extra conductors are needed (which is why I can't just use a usb 2.0 cable). I know that the USB 3 cable has a differential pair meant for USB 2 signals, but for improved shielding, I want to use one of the (shielded) Superspeed pairs for the USB 2 instead. Are there any downsides to this? From what I can tell, the impedance of all the twisted pairs are 90 Ohms.
I'm making the devices on both ends, and they'll have custom connectors, so compatibility with other stuff isn't important. To be clear, the custom connectors are not USB connectors.