A second video card for a Dell XPS 420?

I have a Dell XPS 420 with pretty much maxed out everything, (Of what i could at the time). I currently have a Nvidia GeForce 8800 GT. i am thinking about getting a second video card. 2 questions... 1- do i have to get the same card, 2- is it worth the cost. (My comp runs fine with one, but with the increase in game performances, i think i might eventually need a second card.|||Your computer only has 1 PCI-Express x16 slot so you wouldn't be able to use another video card unless you removed your present one.|||In order to increase your performance down the road you will have to buy the same card. This is because video cards don't normally work together unless connected using SLI. You will have to check if your motherboard supports this.|||Your Dell cannot run SLI as far as I can tell.