As I mentioned in the original thread, the nitrate content of beets varies widely, depending upon both growing conditions and the variety of beet.
Moreover, you would still have to drink the juice from 3-4 nitrate-rich beets to achieve the apparent *minimal *effective dose of ~5 mmol.
Thus, while I would never discourage anyone from eating their vegetables as their grandmother told them to, I don’t think you can really count on juicing beets yourself as a guaranteed way of providing sufficient nitrate to enhance athletic performance.