bad behavior between Opera 38 and Windows 10
I noticed bad network performance with Opera 38 even using Turbo to bypass some bad issues, dropping DNS errors often. I reinstalled network drivers and checked windows updates to discard (even known related bugs on Win10), but still bad.
One thing i suspect is the Opera autoupdate service, which is hopping everytime seeing task manager. Linux side doesn't has this issue.
dropping DNS errors often
Run a continuous ping on your DNS server, does the ping ever spike or not come back at all?
i tested with many DNS with the same results (Yandex, FreeDNS, OpenDNS, Google) and the issue is only worse with Opera. Other internet based apps aren't affected. I reinstalled Opera to diminish the effect but still present.