IT systems are tricky and confusing. All IT equipment should be bonded through its power cord equipment ground. But some IT equipment has external grounding screw lugs. This is most common on network switches as those using shielded cable tend to want those shields separately grounded to an IT grounding bar. In every IT item I ever looked at, I could see nothing in the instructions mentioning that ground lug or indicating any conductors sizes. Many times, those screws were unused, especially if we weren't using shielded cabling.
When we did use them, jumpers from the IT equipment to the bar were the same or larger than what was in the circuit feeding the rack, with #10 being the most common choice. A separate bonding wire grounding the IT ground bar was typically #6 (perhaps using 250.94 as the reason -- no one ever said why). I see no reason to use table 250.66 unless you intend to ground large transformers to it, and the IT people usually do not want to use a "power ground". They used to want Isolated Ground receptacles for everything too, but that seems to have finally waned.
