The graph below now has the original 2 results and in addition i've added results for the NV card using forceware 65.62 then some with an extra GB of ram added to that system, then the result of the card overclocked to its max using coolbits +1gb extra + 65.62. I also reinstalled windows, SP2, Hyperion 4.53, and Source to be safe...
Probably worth noting that all optimisations were on for the 65.62 and i tested with vsync disabled in the driver and app and also aa/af enabled in both to check the results were ok no matter what method was used. Finally, my original findings have been replecated by 2 organisations outside DH.