You know that what Belden and other cable manufacturers give on length are tested under ideal circumstances.. With a connector that also matches for 6G or higher. (Yes you also need higher standard connectors.. The default connectors we used in the 1,5G world have a different di-electrum which causes a lot of dampening above 4,5Ghz.
Also 62 meters under perfect circumstance.. So without
ANY other cable or interference nearby the cable. No power cabling, no other video cables.. No magnetics fields or power supplies near by.. Just 1 cable in lab conditions.
Our thumb rule is cut the specified length by the manufacturer in half. That is the maximum length safe to go for on the road, rental conditions and racking conditions.
Not to say that inputs of Atems and videohubs also have some trouble to recover from the length the cable manufacturer gives.. So Belden can say there cable does 62M on 6G. But that doesn't say it will do that with every device manufacturer.. As Macom, Semtech, Texas Instruments (the 3 leading chip manufacturers in 3,6,12G chipsets) all have different specs for there chips..
Go with a better cable, and appropiate connector that will handle 6/12G sdi.