Yeah you can't base what kind of card you want to upgrade with based on your current card. From the sounds of it though you should probably look into upgrading your motherboard as using an 8x card in a 4x or even 2x environment would just kill it horribly. I tried putting an 8x FX 5700 card in my ASUS board which has 4x and the computer froze everytime, but that coulda been a fluke incident