Someone has offered me an AMD 4870 1GB for $100. I'm currently running an 8800GTS 512. I wanted opinions on how much of an upgrade I could expect. I'm also running a Q9400 @ 3.2GHz with 8GB RAM. I game at 1680x1050. Current games are L4D2, CoD4, Crysis Wars, Demigod, etc. Any opinions would be appreciated.