Low Power NVIDIA GPU for Mercury Playback Engine

[AMD Radeon]

Dear all toms fellow,

i have had a hard time choosing the lowest power nvidia GPU to optimize premiere CS6 mercury playback engine. The only source i can read is here http://www.studio1productions.com/Articles/PremiereCS5.htm
but it is a bit incomplete

afaik, MPE can be optimized with 1GB ddr5 from nvidia line up, but currently GT 640 DDR3 performs similar with DDR5.... so i can see DDR3 version is still viable option

because i love low power solution, these following card are my only option
GT 630 DDR3
GT 620 DDR3
GT 530 DDR3
GT 520 DDR3

GT 520 DDR3 is the lowest power i can see on benchmark, but, can it deliver similar performance with its GT 630 brother?

note : i dont play game AT ALL
and i already had GT 240 1GB ddr5 and GT 440 1GB DDR5, but i am not satisfied with its high idle power, so i look for GT 5 and 6 series

best info with link/bench is really appreciated, will be selected as best answer

 

[AMD Radeon]

i think i am going to stick with my 240 and 440