It was the network after all. I had stretched and bent the freaking network cable in such a way that the autonegotiation made the network speed 10Mb/s, half duplex. This I discovered with ethtool eth0.
The apparent stops I think must have been due to some buffering somewhere. When I looked closer it appeard that the copying was just really slow. I looked closer by enabling nfs logging to syslog with sudo sysctl -w sunrpc.nfs_debug=1023.
How about that?
