in practice, there is no slow down but only acceleration when working with octane-net, because you start with the GPUs in the master then the speed increased as soon as the scene already compiled is transfered to the slaves

obviously if you shut down a slave you have a slow down.
the c4d team render works with the v1.5 also.
i suggest you to leave the xeons and take the money for more GPUs

ciao beppe