After playing a lot of Skyrim I noticed that sometimes, especially in Dwemer Caverns, there are huge performance drops and stutter, the game becomes unplayable and FPS goes to below 5. While this happens the CPU at 100% usage and the GPU load goes to 30%. The reason behind this huge problem is that the shadows are “rendered” by the processor, a childish move from Bethesda. After lowering shadows detail to something lower than Ultra, the issue was gone completely, CPU usage was normal at about 40-50% while the GPU load went up to 99%. I advise those who have frame rate issues to lower shadows to anything lower than Ultra.