Agreed. It shouldn't matter what platform you use, Windows or Linux, as long as you can squeeze at least 600Mh/sec out of your twin 5830s you should be able to cover your electricity costs and then some (depending on how much your utility screws you for power).
A word of caution, however; make sure you have a power supply that can handle what those two cards will draw, and that you don't have too many other peripherals to run at the same time. If you use Windows, run msconfig and turn off all unnecessary services and processes you really don't need to run while mining (e.g., print spooler, volume shadow copies, bluetooth, Windows themes, etc.). I have blown a power supply by over-stressing my system, and you don't want to risk damaging your hardware that way. I now have a 750W PS so I shouldn't have to worry about that any longer, but my old 400W power supply is now in the hardware graveyard, thanks to overclocking my 5850.
Or just buy a bigger PSU?
Lol if you're really worried about power saving that much, start by disabling devices in the BIOS. Miners don't need wifi, audio, secondary sata, etc.
