For the money, you can't get much better than that. Come up with another $50 or so and you'll be able to buy a Bulldozer chip when they release mid-to-late September, and that will drastically improve performance. Once you have the cash to do so, buy another 6850 and run them both.
With all of that, you'll probably be able to run BF3 on med-high settings. With your current build, probably low-med... which still looks great
saves you $40 . Its still AM3+ . Most of the difference is the pci-e x16 slots running at 8x/8x when you crossfire . All intel sandy bridge boards do this and it doesnt seem to affect their graphics performance .
You can save more by trimming the RAM back to 2 x2 gig .
This wont affect gaming performance , and is unlikely to make a huge difference to video editing for a casual user