What's your controller setup? Because at 250MHz you should be seeing 110GH each.
The units are fluctuating between ~95G and ~140G the average is slowing climbing. sitting at just over 101 each right now.
Im running 3 off of a laptop, each in its own USB port right now. It might be the Intel USB 3.0 controller if that still effects the Terminus as well.
I'm seeing a daily average of 195G with 2 units at 225Mhz on a PI3, which is pretty close to the expected 99G/unit at that speed.
How many USB ports does your laptop have and how many internal controllers? If you have all three on the same internal hub, could you be hitting the limit of the USB controller?