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Congrats on getting the 500. If you're on a budget, you might want to consider a wimberley sidekick. I use one with my 600 and find that it works fine for me. Lens motion is smooth, and balance is perfect with my 5D3.
Another benefit to the sidekick is that you can easily remove it and revert back to using your ballhead, if you use one. A dedicated gimbal would require switching out heads.
+1 I find the sidekick with a BH55 more than able to handle my 500 and 1d4. As stated, it's a quick switch back to just a ballhead if needed.