This is exactly what I was looking for!!
From this, I can see that the cards are more or less comparible - it all depends on the game. The GX2 might be ahead alittle.
The most important page was the one with the resolutions. I have a huge monitor that runs 1900xwhatever, so the 4890 might be better for me.
Please remember that this is a warranty replacement. So I dont have the choice to upgrade. I can only get one of comparible value.