Thank you all for your reply.
Actually, the same 16GB takes 31 min. If Gbit is 10x faster than 100 mbit, I expect that the transfer speed is at least 2x or 3x faster.
As for Jumbo frame, I have seen some posting saying that DIR-655 doesn't support this feature.
The cable from the PC to the router and the router to the DNS-321, they are both CAT 5E.