I put together a new build a couple of years ago and have recently returned to playing WoW. I figured, with it being such an old game and all, I should be able to crank up the settings and really enjoy it.
However, I am finding that when I throw the settings up to max on 1920x1080 (My preferred resolution if poss) I am getting frame rates of around 15fps, even when not around other players.
The 4850 really is only very capable at any resolution below 1680x1080. Your tech is also pretty old so I'm not surprised its showing age. Most MMORPGs need a quad, bbut the E8400 is defiantly a good enough chip. The main thing is mostly your GPU. Adding another 4850 would help if you have another PCI Express 16x 2.0 slot available. That or buying something like the 6950 1GB for 250$ would also help. Otherwise you could keep this as a backup and just start a new build all together.