I've experienced this issue a handful of times accessing the DNS-343 from a Windows 7 PC. 97% of the time the unit has good throughput, but on a rare occasion drops to the ~600kb range. When this happens, rebooting the PC typically always the problem. Again, these occurrences are so infrequent, that rebooting doesn't bother me that much.
I wasn't aware that this was caused by a driver issue.