The quality settings ultra in FS 2 are now about medium or even low in FS 4. We've shifted the quality settings to make better use of the newer graphics card. So don't be fooled by this please. Medium is the old Ultra if you will. Doesn't mean it is performing badly just that you selected to high of a quality setting.
But, I have tried low quality in various screen resolutions as mentioned above and still not smooth like I expect it to be. Its my video card. It doesn't have enough memory (as per specs) to run it. I am aware that it has been said several times FS4 is to take advantage of modern video cards and that I would have to run the SIM in a lower quality setting due to my video cards lack of capability. No other option but buy a new *modern* video card.