Well, your video card has four times the memory than mine and I don't experience stuttering.
So that leaves your processor speed, RAM and your ISP. My processor is decent, as is RAM but my saving grace is my cable averages 11MB download so my ISP overcomes any deficit that my computer has.
What Paddy was asking though is for you to list in the sidebar under your avatar all the basic info regarding your Macs. You'll note Paddy, kbear and I all have several Macs and their specs listed. Go to My Controls at the top of this page, then to Edit Profile information. The My Macs at the bottom is where you input the specs. Don't forget to click on the "Amend my profile" button.