This is the main reason why I could get my OC to 700 core on my asus card.
Raging Cain is working hard to figure out how the gtx 590 works. it terms of PDL or power draw limit. He has posted on the nvidia forum on the issues with pdl and why some games are determined by pdl. I highly doubt he will get an answer but I commend him for trying Just like I did with Nvidia locking down the voltage with in the drivers and trying to find out why
here is the thread tons of info plus modded bios as well all for free
http://www.overclock.net/nvidia/1063263-gtx-590-flashing-overclocking-thread.html