For the past couple of months I have been really disappointed in my PPD numbers. I tried several things to improve matters with no success. I hooked up with another GTX 680 owner over on the F@H forums for some advice. Good thing I did. After trying several things he concluded that my version of the client had issues and suggested I finish the WU's I was on and then remove the client and do a fresh down load and install. For some reason my client got "stuck" with the CPU locked into just using two cores of my i5-3570k and my GTX 680 only running at about half of what it should.
I did so earlier today and presto I am finally getting x17 WU's which I had not gotten at all even after setting the client to advanced over a month ago. Plus my CPU WU's are running faster, or so it seems to me. It will be interesting to see what kinds of PPD numbers I put out now.
So, if your not seeing the numbers you think you should be getting you might giving a fresh install of the client a try.
Almost forgot to mention, I also rolled back my Nvidia GPU drivers to v327.23. Anything newer and OpenCL takes a big performance hit, hence slower folding.