I would really suggest getting a new motherboard and CPU and putting it into your system. That motherboard/socket is about a decade old so there aren't really any cpus that will be and upgrade.
If you can tell me your budget for a motherboard/CPU upgrade, I can recommend something. Even the lowest end CPU from the past couple years will easily beat the best CPU for that socket. Not to mention that it will stop recipeiving updates and you cannot use newer versions of windows.