Quote - I do have texture filtering set to "none" on some Image map nodes... set to "quality" on others. What are the implications of that? 

Disabling texture filtering dramatically reduces the efficiency of the texture cache. When using large textures, this can result in a lot of disk access from the renderer, since it has to load new texture data constantly. Since only one thread at a time can access the disk, render threads can end up spending most of their time waiting until it's their turn to read texture data.