Try this to check the status of Receive Window Auto-Tuning Level
netsh interface tcp show global
and if it is disabled, turn it on with
netsh interface tcp set global autotuninglevel=normal
This helped me and two mates. The settings need to be run with admin rights cmd (and shift+ctrl when you run it).
As far as we understand it you would most likely want Receive-Side Scaling State enabled as well.
netsh interface tcp set global rss=enabled
We have not tested Hamachi after changing these settings. Nevertheless, just wanted to share because this problem was making us crazy.