Mobile processors are in general not as powerful as desktop versions, because they have to run cooler.
Same for the GPUs.
Both the x4 955 and 965 are black edition, meaning they can be overclocked. Don't pay too much more for a 965, but if prices are similar the 965 will run a bit faster out of the box.
The idea here is to get you enough CPU on a good platform, and maximize the GPU budget, as that is where you will see the most gains at this budget level.