Hi Jaka,
Apologies for the delayed response. I am awaiting a second usb cable -- however, I don't think this is the source of the problem given that every thing works fine with the cable and one of the cameras i.e. the only variable is the camera change results in the slow down … which makes it most likely that either there is a hardware fault with the camera or there is a software setting (hopefully) that can be updated / fixed.
I have also verified the same behaviour across a PC running linux, windows, and a raspberry pi (albeit with a single cable).
Thanks for the assistance.
Best regards,
John.
PS I will update once I have the second USB cable.