Telyko, ha! Yes, I was not clear at all. It certainly appears that the driver could be optimised to run external, and perhaps more modern, hardware. Have you tried turning webgl off in the editor and seeing if that makes a difference to the laptop performance? On my older laptop I found even just having webgl on made a huge difference, even with no shader effects.
That would still not explain why the driver is not running each screen the same. Perhaps it self-allocates more memory to running another monitor and that just happens to be what node requires. If you can manually set how much memory the driver uses then, perhaps, increasing that might also help.