@nucanuca,
I guess you have no idea what you are talking about. GTX 580 is Fermi based. Fermi was the last architecture that nVidia did not cripple for acceleration. Kepler had more or less double the CUDA cores of comparable Fermi card, running at lower speed (the CUDA cores run on frequency different than the GPU itself). Sadly nVidia crippled all Kepler and above architectures via drivers for professional software acceleration. All Kepler GTXs barely reach 50 or 25% load in Premier during load. In a lot of benchmarks GTX 580 beats 680 and 780 in acceleration. A lot of users even complained in downgraded performance when going from 570 to 680. nVidia made the 500 cards a beast of an accelerators so it cut their Quadro sales. If you don't trust me - go and search on other websites. People specially using Premier still hold to their 500 cards specifically for this reason.
And just to end it up:
http://www.pugetsystems.com/labs/articles/Adobe-Premiere-Pro-CS6-GPU-Acceleration-162/
Do your research, test it by yourself and then talk. GTX 580 is a very different case than a 600 or 700 or 900 series. But sadly, you cant buy 580s anymore, else I was going to first in line.