I have the Markins M-10L ballhead. It is amazing, absolutely no slippage and the camera stays locked in all positions.
I use it with all my lenses up to 70-200 2.8 and including the 100-400.
Very stable and a joy to use.
Just for fun, I mounted my Sigmonster (300-800) on it and it was surprisingly usable. (not as good as a gimbal of course)
My friend has the really right stuff 40 and I use it sometimes. To me, the Markins is superior, smoother and easier to operate.
I have to say that the RRS clamp is great.
If I had to do it again, I would buy the Markins M-10L without a plate holder and get just the RRS clamp to put on it.
That would be the ultimate combo.
Good Luck.
Jean
Lots of equipment, no money and no time.
1Dmark IV, 1DmarkIII, 5D. 17-40L 4.0, 24-70L 2.8, 50 1.4, 70-200L 2.8 IS, 85L 1.2, 100 2.8 macro, 100-400L 4.5-5.6 IS, 300L 2.8 IS, 300-800 5.6.