What resolution are you playing?
But keep in mind, what you are asking is impossible with 400$. You need to update your CPU (so your mobo so you RAM) because it is your biggest bottleneck right now.
Forget the HDD unless you really need to.
To max out FC3 at 1080P, you need a graphic card that cost more than 400$ (or 2 GPU that gonna cost as much).
You know that FC3 look great at low-medium settings too?
I'll keep my last suggestion, focus on CPU/Mobo/RAM, wait some month, than get next gen graphic card.