Thing is that 40Gbps is only 1.25x the bandwidth of x8 PCIe gen2 speeds. Accounting for USB overheard I wouldn't be surprised if it was equal or just barely above x8 PCIe gen2 bandwidth. Remember on release of the RX6500 it got flack for being x4 only as it got a huge perf hit on x4 PCIe gen3? Note that x4 PCIe gen3 happens to be about the same bandwidth as x8 PCIe gen2. 40Gbps is pretty tiny, esp if there is overhead to deal with.