I took the advice of my DAW builder, VisionDAW, and installed a 10GB Ethernet Card, Intel X540-T1 (about $290 from B&H Photo in NYC). For my purposes, It isn't for achieving higher bandwidth, but for its onboard processor that helps distribute the workload better from three incoming LAN connections from the gigabit switch.
It helps. I can now, at least by my initial tests, operate at 256 samples latency without asio overload.... BUT I must have the Cubase Asio Guard 2 turned on and set at "normal" to achieve this. I could not, before. I would get at least some occassional asio spiking. But not now. This Ethernet card helped things just enough. I have about 32-36 incoming stereo busses among the 3 computer slaves.
Paul