I think you will find that the numbers relate to the version of core design. From memory, one is the Palomino core and I think the other is the Thoroughbred or Morgan (although I think the Morgan was Model 7). You should be able to find this info somwewhere on the AMD site (thats where I saw it). I believe that the model 8 is only compatible with latest boards. I will have a look and see if I can find this info, but have another look yourself, I'm sure its there somewhere.