Your specs are definitely OK. In my setup I can saturate 1Gbit/s LAN with slower hardware.
But in general transfer speed is highly dependent on the files - large files are expected to transfer close to hardware limits, lot of small files could be significant slower due to application overhead (e.g. read/write to the database).
Review you NC config - some apps are known to slow down the system e.g. external storage. Start with really basic system and and functionality slowly to nail the problem.