For testing purposes, try placing your PC and DNS-345 on the same switch and remove the router to eliminate any other possible conflicts. You may also want to test another client PC to rule out any PC NIC related issues.
I've achieved a maximum upload speed of ~45-50 MB/s (not mbps), but upload throughput usually hovers around 35 MB/s (I can't explain the delta). I see the best results when the host and client are on the same physical switch.