When copying directly with the 643 (version 1.10) between my Maxtor (100) and Buffalo LinkStation Live (1000) I get substandard performance (400,000 - 1,500,000) as told by TaskManager. If I copy from either NAS to my laptop, in either direction, I get from 8,000,000 to 11,000,000. Also just upgraded to 1.11 on the 655 and a funny thing happened. On my first try I was able to get 5mil and I was thinking its not great but... Every other test after that was back down to substandard.
Doing a direct copy with a wired 100BaseT connection got me 11,800,000. I've tried many permutations of Beacon, WMM, Short GI, wireless protection, QOS enabled, traffic shaping auto/manual to no avail. Always used WPA2-PKA/AES Wireless N only.
643, using 1.10 because I was getting bad throughput in the same room as the router with 1.20 (dropped to 400,000 for 3-8 seconds every 8-20 seconds). Tried a bunch of combinations before I backtracked. Both Maxtor (Shared Storage+) and Buffalo have the latest upgrades. The Buffalo has option to use jumbo frames but has always been set to default (1518).