Best of luck.
I've gotten consistently excellent results with the 500 f:4 L IS lens using the Sidekick on a solid tripod, even with the 1.4x converter. I generally carry the lens in a Scope Pack, as the side pockets are perfect for the Sidekick and teleconverters.
Back in my film days I used a Pentax 600 mmm f:4, which weighed 16 lbs. plus; this monster required something more substantial, and worked well on Kirk's "king cobra" gimbal mount, similar to the full sized Wimberly but a bit more compact.