You can almost double your profits by spending 300 on a 7950 (~600 kh/s) instead of 160 on a 7850 (~320). You'd also have a card that will be easier to sell back in the future (IMO) as the 7950 is a much superior video card. The 7850 w/o crossfire is already struggling on some of the newer PC games.
I might do that. I just have to wait a bit longer to get enough. I'm still using my trusty old 560ti for games 
So you think the other parts are fine? Will I need more RAM? RAM is cheap as chips, so I don't mind that.