OP, I'm having the exact same issue! I bought a Visiontek 7970 and I had problems with artifacting for about a while right out of the box. I downloaded the latest AMD driver available at the time (as of July 18 2012). I happened to capture a pair of instances where I was able to get some video of what was going on. The first one is kind of long because I had seen other artifacts that I caught with the second video that I was hoping would show up in the first:
http://youtu.be/UB3FHWZUWM8
http://youtu.be/bBSLGjueGVc
It just so happened that AMD put out a driver update soon after and the artifacts stopped, so I chalked it up to a wonky driver. My machine specs for comparison:
Asus AM478T-E mobo
1100T @ stock
8GB Corsair Vengeance @ 1600mhz
Visiontek 7970 model 900556
Win7 x64
I am now running Win8 x64 and I'm running into the same problem you're seeing. I just tried BF3 maxed out at 1680x1050 and I was getting 60.6% GPU usage and 80% CPU usage. I tried to run the Sleeping Dogs built-in benchmark earlier at the same res at High with both vsync and the fps limiter off and the GPU maxed out at 26%; I can't remember what the CPU was at, but it certainly wasn't maxed out.
I am suspicious that my mobo may be causing the problem since drivers were last released in 2009 and they refuse to work with anything but win7.
I hope something I mentioned was of some use.
Edit: I forgot to mention that I am running dual monitors (kinda obvious from the videos). I just thought about mentioning that because I learned right after I got the 7970 that 7970s with two monitors have a very high idle temp(around 60c), which I would've never guessed would be the cause. Maybe something seemingly unimportant detail will help us figure this thing out.