There is also the option of getting a 6950 2GB. It's $229 + Free Shipping / Before $30 Rebate. Even this is barely a significant performance gain; maybe 25% in best case scenario in specific games. Your current 5850 as it's still a very capable card and can run most modern games at high/medium settings up to 1080p. I would recommend you to wait about a month or two until Nvidia and AMD release more of their mid-range cards [i.e There is nothing in between the 7770 and 7850 - HUGE performance/price gap here and the lack of the 660TI on the market playing field]. Sorry to disappoint you but until Nvidia and AMD offers more options and possibly drop prices, there is no worthy upgrade at the $200 mark.
I agree with coffee. I currently own a Sapphire 5850, and am looking to upgrade. I don't think the jump to a 6950, or any currently priced $200 card is really worth it. You'd need to move to a 7850 or better imo, and those run around $250-300. For 5850 owners like us, upgrading requires a significant bump in price. We really need to get into the $300-400 priced cards to really make an upgrade worth while.