We have tried Fedora, but it couldn't detect the monitor resolution and the GNOME 3 experience is seriously lacking.I can only speak for the 2500K i5 which has Intel® HD Graphics 3000 (While all the others have Intel® HD Graphics 2000) in saying that graphics performance here is fine using the current stable Fedora release fully updated. No issues to speak of.
You can save yourself the cost of buying a card if you switch to Fedora or (I would hope,) use a Ubuntu daily until the next Ubuntu release.
Although I know the HD Graphics 3000 are formidable, the 2000 are simply inferior, any of the cards I listed outperform them greatly.IMO you won't get much more than a little if any better performance than HD Graphics 3000 with a cheap add in card.
Yeah, benchmarks on AMD cards are very positive, I'm a bit worried about driver support in the future, though.If you really must use Ubuntu as is before they release anything as stable which works with second gen i5 processors, without going for one of their development CDs, then an AMD HD card is the right choice. The higher the number the better. I would avoid second hand unless the price is extremely reasonable and the source is reliable.
ATI\AMD make the most powerful graphics cards in the world. And have done consistently for as long as I can remember.
Except for KMS, we haven't, in my friend's old PC. Granted, those were old cards (GeForece 5200 and 6200).I have had problems with cheap Nvidia cards. Especially using Linux.