I didn't read the whole thread, only the few first posts but anyway.

You can't really say how much card is held back by the memory speed or GPU speed. It depends on the game/app and settings used. High resolutions with AA/AF require more bandwidth than low resolutions without them. Thus one can't really give any kind of percentage estimates that would apply in all apps/games. It depends so much in the game/app. For example in Company of Heroes my 7300GT is very badly GPU bound, giving very linera FPS increase as I increase the GPU clock. Then in Trackmania Nations Forever the same applies for memory, but not for GPU. I can underclock the GPU from 500 to 400 without big FPS drop, but if I underclock the memory from 500 to 400, the performance drops by almost 20%. Oh, and ATITool's 3D Cube FPS seems to scale well with memory BW.