That is an important correction. The speed for the "60 minutes rule" comes from the PERF section of the airplane manual. But you are allowed to pick any realistic one, and then apply with the CAA to have it authorized.
That is of utmost importance for LROPS A/C, where a very high OEI speed is desirable to increase the range circles for crossing uninhabited territories. At the cost of the extra/additional fuel expense where required.