Im playing on Ultra without any Mods.
If I play on high, it will increase the FPS by 2
I fail to see that I have to play the game on settings under ultra. Every game runs without a problem in ultra, except skyrim.
because your computers not fast enough
simply put if you run the shadow setting too high for your CPU it'll hold the games engine up from passing instructions to your graphics cards at 60FPS
also i already know your graphics card cant run ultra shadows without the graphics card running out of headroom, i had 2 of them and 2 wasnt enough for ultra shadows, maybe it would be OK for 10% of the time in small spaces like indoor cells, but thats only a small area of where you experience skyrim
as skyrim uses a different engine to BF3, you cant compare apples to oranges. And because of the way skyrims programmed, ie shadows being linked to CPU speed you'll need to configure it to your hardware
if you dont want to see a moment's lag, and experience a perfectly smooth skyrim with no performance dips i'd use the high preset and drop shadows to medium (if you overclocked your CPU you could run high shadows perfectly)
goto markarth to configure the game. Markarths a high geometry high shadow area if you can run it there with not a microsecond of stutter you'll be good for any other area around skyrim and you wont see any dips in performance