No you cannot. You would have to get another 6850 to crossfire them. You can crossfire different brands though. (MSI, GIGABYTE) etc..
100% wrong. you can cf any two cards with the same first two numbers in the name. it isnt ideal though as only some game support the use of both cards at full specs and even in the games that do you are likely to experience microstutter.
didnt i just answer this question a minute ago? why double post it wastes peoples time.