i have sapphire 4890 core clock 950 Mhz. It can still handle most game @1680x1050 res, but i really want dx11 card. Do u recommend something like ati 6850 or nvidia 460gtx or should i go for a bigger gun, like nvidia 560ti or ati 6950 1gb?
You've just answered your question, HD 6850/70 will do just fine and max out some games at your resolution.
GTX 560Ti, HD 6950 will be overkill as well
6850/GTX460 isn't that much faster then your 4890. Even the GTX560/6870 won't feel like much of an upgrade. You really need the GTX560TI or 6950 to "feel it".
I just bought http://www.newegg.com/Product/Product.aspx?Item=N82E16814161372 (HIS Iceq edition 6950) a couple weeks ago as an upgrade from my 4890 because I wanted dx11 for BF3, and to be able to play more new games coming out soon on max settings. I do not regret my decision at all. I would recommend this card to anyone, I absolutely love everything about it