If your not concerned with performance, 20 Gbit/s thunderbolt != 8 drives @ 6 Gbit/s (42GBit /s) i think a modern raid card can deliver 8gbit/s over 8 PCIe 3

If your not concerned with performance, 20 Gbit/s thunderbolt != 8 drives @ 6 Gbit/s (42GBit /s) i think a modern raid card can deliver 8gbit/s over 8 PCIe 3 lanes However i guess you could trunk a few together?