When playing The Witcher 2 on my laptop, I can only set it at medium graphics without lag, but then there is no lag during movement and normal play. With my desktop, which has better specs, I can set it at high or even ultra without lag, but every time the character moves, such as swinging his sword, the game becomes unplayable until the animation is over. The laptop has the same amount of RAM, but a 7200 RPM hard drive while the desktop has a 5400 RPM (and it is mostly full). Would such issues be cause only by hard drive speed or could there be another factor? I have noticed this in other games too, such as Infamous, where the world is continuous and has to load as you play.
ATI Radeon HD 5870
6.00 GB RAM
Intel Core i7 Q740 1.73 GHz
7200 RPM 500Gb HDD
Both Windows 7 64-bit
So where is the problem? if i understood it right, you are saying that on higher specs, there is more lag...
But the question is, when you set it to medium on the desktop, is there lag? maybe one of the options you are adding like motion blur,super sampling, or something, is what causes the animation lag... you need to tweak the graphics removing this specific effect... if you have this lag on the same specs than notebook, then you could say something was wrong... your video card can handle more graphics. but not as much as you think, you need to tweak that...
i don't belive HD speed will influence in that.
EDIT: now i read that hd is almost full, try clearing some space, at least 10gb free. i already experienced lag in witcher 2 when my hd was totally full.