I have a pair of AMD Radeon 5700 Series cards (apparently released in 2009!), which seem more than up to the challenge. One thing to consider is that with 2 graphics cards, you needs at least a 550W power supply (I had a 500W power supply that died trying its best).

Unfortunately my carpentry skills lacking, and the Dell Single Monitor Arm [1] are NOT suitable for mounting 2 monitors on top of each other (not enough height).

[1]: http://accessories.us.dell.com/sna/productdetail.aspx?c=us&l...