I had exactly the same issue with my 4870x2 and Fifa. I found a fix for the stuttering but to be honest it didn't make it completely issue free.
Google Fifa 11 stuttering and they're are a lot of threads around on it.
Here the one I used for the fix:http://forum.ea.com/uk/posts/list/8811.page
It seems to be quite a widespread issue and I guess it's driver related. In the end I gave up playing it as it gave me a headache!
Let me know if it helps