Does it work well with AMD processors I just read the push pin system really sucks?
Yes, I am planning on running 4 cards in crossfire eventually right now just have to stick with 2 plus will see how the 4870's are price to performance but eventually I will need the extra power in the PSU.
heres the general rule of thumb for added performance with added cards, if your talking games that scale up faily well. in some cases a single card outperforms multiple cards.
adding a second card boost performance by about 50%
adding a third boosts an additional 10-30% many games get little to no performance gain from the third.
adding a 4th boosts by less than 10% most games are not helped at all by the 4th.
Idealy youd see +100%, +50%, and +33% for the 4th. so you are far from getting your moneys worth with crossfire or SLI