I built my PC with a mid range AMD Radeon 6850. Everything worked well as long as I worked in Windows, or even Mac OS X for that matter. But the day I switched over to Ubuntu, all hell broke loose. My crime? Dual Monitors.
Jeez, my macbook runs dual monitors on Ubuntu and OpenSUSE without a hitch, and it doesn't even have a discrete card! Here’s my verdict based on personal experiences trying to get a workspace ready.
Unfortunately, I had to give up one of the monitors soon after I got my new KDE workspace all set. Till I wait for a new one to arrive, you'll find KDE can do absolutely anything you want. And it looks super good! Thanks to the beautiful Plasma Desktop. Damn it's pretty :)