I see, thanks Mark. Anytime I shoot something in motion, I quickly take the lens off the head and do it handheld.
If you're good enough to do that, which your photos indicate that you are, no real need for a gimbal 'til you get a lens too big to it with. Only once have I owned a lens significantly larger/heavier than a BigmOs (Nikon 300 2.8) and that was for a short time when I was experimenting on with Nikon. As a Canon shooter, I've never had a lens as big as your Sigma, so I almost always hand hold... with the exception of going to a destination place like LD14 for BE's where you sit/stand in the same place for hours on end.