From the thread:
The ones marked in red just cannot work under certain dotclock values and therefore the minimum displayed resolution is limited by it. There's a workaround for that which is explained in the Video Mode Maker section, but we particularly recommend the following video cards in case you can choose, since they have been confirmed not to have any low dotclock restrictions
So if you don't want to run into issues, just grab one of the cards not in red. I have run with a 4870 and now run on a 4350. I think I paid 15 bucks delivered from ebay for the 4350 after the 4870 started having artifacts.
5000 series (and newer) are not supported and likely will not be due to the driver changes as Calamity has mentioned before. Just grab a cheap 4000 series and run man. You will be glad once its all running.