so i would assume, because it's not an actual 10/100 ethernet, that it would run at (saturate) the full 480mb/sec of USB2. so not quite GbE speeds but pretty damn close. yay!
Based on what USB2 gives us with "mass-storage" devices, 30MB/s is basically the upper bound. And FWIW, when I connect my desktop to my A20-based router via USB2 on one side and USB-OTG on the other (using the "gether" gadget), I'm getting about 10MB/s, so "faster than fast-ethernet" maybe, but be surprised if you get "close" to GbE speeds.
Stefan