The catalog and brochure state the 6Ks servo update rate as "as fast as 62.5usec per axis." This may be confusing, but it is accurate. The actual rates are:
For example, axis 1 on a 6K4 will be updated within 62.5usec, then axis 2 within 62.5usec, similarly for the remaining axes. Thus, by the time it is axis 1 turn again, 250usec has elapsed. So, each individual axis gets updated at the above rates.