Hi,
I would say with two 4850 x 2 video cards the 6000+ processor could be a bottleneck, but this is probably true with most CPU's, or all currently (lol). I would also change the post to "Two 4850's in crossfire" because some people may think there is some crazy new 4850X2 dual-gpu card or something (I had to check newegg lol, apparently I am a n00b). The 6000+ is still a great processor, so I would say try the system, and if you are not happy with the performance; it's likely due to the processor, and then look at upgrading. There is no point in ordering a new motherboard + CPU + RAM if the "Crossfired" 4850's work great in your current setup. Worst-case scenario; you get the two cards running, the performance isn't what you expected; so you go order a new processor for $30 less than you would have if you ordered at the same time as the video cards.
My two cents.
Best of luck,
dg6464