XVM tends to cause FPS drops. But your PC should be able to handle it.
Can you try to remove your game preferences file and reset your World Of Tanks settings back to default.
To perform this, please perform the following:
Hold the Windows key and press “R”.
In the Run window, type or paste “%APPDATA%\wargaming.net” (without the quotes).
Delete the folder named WorldOfTanks.
Afterwards, simply launch the game. Also, this will delete all settings. Including login info.
That might fix the issue. Other than that, try with G-Sync off. Not sure, but XVM may not like it.