What are the issues? Is it just RAM related and does the number of monitors matter? Or is there something else specific to the GPU?Machines running Sandy Bridge processors have issues running High Sierra when they only have 4GB of RAM, upgrading to 8GB fixed said issues - It's GPU related. Less RAM means less RAM available for the internal graphics, etc.
My old Penryn laptops from 2008/2009 which had 4 GB had a dedicated GPU with GeForce 9400M. That had its own 256 MB RAM, sufficient for the internal display (and the occasional projector as a secondary display). However, they've since been updated to 8 GB anyway, since 4 GB RAM is limiting in High Sierra even with a dGPU.