This is my old friend back from when i was working as the action photographer. The Canon 1Dx has always just worked and the Canon 500mm f/4.0 IS is stille the best lens for me.
My old setup has got an upgrade because it is on a new mission - Eagle photography in Sweden. And to handhold a Canon 1Dx with 500mm f/4.0 IS + 1.4x extender or 2x extender is really hard. So I got at Sirui gimbal to hold it all.
And of cause the very stabil ReallyRightStuff Tripod TVC-45, which extend to 216cm, and can hold 45Kg