How fast can a SHA-256 implementation go?
Ryzen supports special instructions for SHA-256, achieving 1.9 cpb on long messages according to eBACS (graph). Assuming a 4 GHz clock, this corresponds 2.1 GB/s, 17 Gbit/s or 30 ns per block.

From the 22.5 cpb value for an 8-byte message (a single block), we get 180 cycles per block, 2.8 cpb or 45 ns for a single unpadded 64-byte block.