What power supply is that?
Given you have a good reliable power supply:
Gigabyte P67 board (SLI-ready)http://www.newegg.com/Product/Product.aspx?Item=N82E16813128478
If your power supply is good, I'm thinking:
These upgrades are going to put around you right around $1000.
Look...You have $1000 to work with. Now is the time to go for something that will take you through the next 3 years and give you incredible video capabilities (you could always get another for your next upgrade and run them in SLI!). The single Nvidia card is awesome plus you will have a new system architecture you'll be able to roll with for the next 3-5 years. You'll be going from a lower-end system to a high-end system by doing this.