What you have now should be plenty ,if you just want to go to one card then I would go with a GTX-670 since it just a hair slower then the GTX-680 and will use less power then one HD6970, over a 100watts less at maximum.Plus it will have plenty of power for B.F.3 at max details at 1920 x1080.Plus it runs very quiet.The Gigabyte or the ASUS IMO
NVIDIA GeForce GTX 670 2 GB Review | techPowerUp GIGABYTE GV-N670OC-2GD GeForce GTX 670 Video Card - Newegg.com ASUS GTX670-DC2-2GD5 GeForce GTX 670 Video Card - Newegg.com