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RADEON RX 470 4GB connected via "Razer Core" eGPU (USB3.1c/Thunderbolt3/40Gbps) produces 550 h/s.

Is there anything I can do, other than OC, to increase h/s in Windows?  Since I value power efficiency, I use -a 2 and No-OC; however, even though I tested several -a # settings, they all produce 550 h/s.  I am using the latest Catalyst beta drivers.  I assume cryptocurrency mining consumes little bandwidth or memory?  So, PCIe splitters and low-memory GPUs should be cost-effective and have little effect on h/s?  Finally, just as a brand/miner comparison, I swapped in a GTX 1080 FE to test with ccminer and it only produced 350 h/s.