Okay... This took me a while to work out, but I think I got it sorted.
Basically, as Durante mentioned earlier. ATI cards have problems when under low usage in that they throttle themselves between frames. This causes a cycle where the frame-rate constantly drops. This can be resolved by setting the graphic settings incredibly high, however this causes slow-down in the game when busy as you end up with no headroom.
By setting the game quality at normal levels, and having a background process use the GPU, you can have a much smoother frame-rate.
AMD fix for high end Radeon cards! (7900 series)
1. Download RadeonPro
here.
2. Download FurMark
here.
3.
Configure RadeonPro to limit the FPS of FurMark to 60. This is important otherwise it will use up ALL your GPU.
4. Whilst playing Dark Souls run FurMark in the background, at an approriate window size. You are looking to have 30% to 40% GPU usage as a ball-park.
If anyone knows a more suitable program than this than FurMark, please suggest.