WD2000js Sata II, time to upgrade?

Hi all,

The use of my computer is quite limited, office applications, code videos, play latest games, etc.. O

So, I update my rig 2 days ago (Q6600-Maximus Formula) and find out that the bottle neck is my HD. ;(
And I noticed that while i was uncompressing some files and coding a video, my cpu was only working at 20% top, my memory was consumed, but not all of it, and the HD was crawling....! ;(

I recently installed windows and it was defragged, so i think it could be the HD.

Now, I'm totally out from the HD world, and i wonder if its time for me to upgrade my HD and if with the options i have, i'm going to see a difference.

Money is not a problem, but i will not pay 200 dolares if i'm going to gain only 10% of performance

Can someone point me into the right direction? Should i get a 10krpm drive? is still sata II the latest technology?
Raid 0 i dont think could be an option, i read the gain is not really something! ;(