I've checked SMB vs SMB2 throughput downloading a large file from HDD attached to RT-AC68U
SMB: 60MB/s. Almost full CPU and MEM usage (Core1: 75%-85%. Core2: 100%)
SMB2: 45-50MB/s. Occasionally it slows down to 0-1MB/s during seconds. Similar CPU/MEM usage (Core1: 60%-75%. Core2: 100%)...