Found the forcing DX11 trick, which seems to have worked.
I've found that the lag is completely gone when I reduce the resolution to 1280x800, though it seems like a massive shame since the 3D part runs perfectly at the previous 1920x1200, so there's clearly something wrong with the UI.
خدمة دعم العملاء من خلال UserEcho
Found the forcing DX11 trick, which seems to have worked.