ETH requires little actual PCIe bandwidth. The numbers you quote are the theoretical max of the channel. Some algorithms may require more bandwidth than ETH. I remember ZEC took quite a bit more PCIe in the earlier days. I'm sure with all the optimizations over the last few months, the requirements of the channel have gone down
Not sure what to look at in GPU-z or any other hardware sensor program to figure out how much speed the PCIe slot is using.
By the look of things, all these GPU's exceed PCIe x16 3.0 speeds now
Maybe ETH uses little but that may be one exception. Just because many people are using x1 risers on 3.0 boards and probably a few 2.0 boards doesn't mean that the 1.1 will work. Those are old motherboards and most people buy 6 GPU boards and build mining rigs gound up from newer product listings