Yes, budget would be useful. Also what is your monitor resolution?
First: Do you need to upgrade it? Are games slow already? If it's doing well enough now then wait until it isn't and then you'll get the newer faster hardware.
But if you need to upgrade, here's some general advice: If that's a BE chip, then OC it. Then go for a new GPU. Again, not knowing your resolution, if it's 1080p then your 6850 is your gaming bottleneck. I would not Xfire the 6850. Not knowing your budget, I can't say for certain but I would buy a 7850 (minimum) or 7870 (or higher) and sell the 6850. If your CPU starts holding you back then upgrade to Vishera and you'll be rocking everything.