I'm building a new system with phenom ii x3 720 black edition and GIGABYTE GA-MA790GPT-UD3H AM3 790GX HDMI ATX AMD Motherboar. As for graphics card, I am thinking of ATI 4670 1G or Geforce 9800 GT 512M. For ATI 4670 card, can I crossfire it with my onboard HD3300 graphics card? How much performance improvement could there be? And, I know with 9800 I won't be able to crossfire. But if considering using only one graphics card, is 9800 a good solution for an AMD platform? Will it outperform the 4670? Thank you very much!