What is my bottle neck?

[Shonumi]

IR should match the windowed resolution if you set it to "Auto (Window Size)". But you can have a low IR and still set the Fullscreen Resolution to something high. Dolphin says in the Fullscreen Resolution description that changing those values has a negligible effect on performance. I'm not sure, but I think this is due to the fact that Dolphin scales the image with Fullscreen Resolution, whereas Internal Resolution changes the size of the actual rendered scenes and puts more strain on the GPU.