Separate GND for both SDA and SCL I know about ground loops and how to avoid them. Aside from a I2C Mux, all the leads terminate in either a 9DOF or a 6DOF IMU.
I've read your article on "How to make..." and page 60. I might have chosen a different coms method if I had read your How to before my purchases. Noise and performance may force a coms change but since I've already spent $100+ I may as well pursue the current course until I hit the wall. As I am still at the prototype/proof of concept state, change is almost inevitable.
thanks for your continued input.