It depends on what software you are using, and what you do with your PC.
If you are using apps that use a lot of RAM (e.g. Photoshop with multiple large images) then you need as much RAM as you can get, regardless of if it is marginally slower. Because any RAM will be 10x faster that swapping to disk when you run out of RAM.
If you aren't fully using the 2GB you have today. Then the extra speed is better. And you shouldn't give up the dual channels.