I'd go with the nForce3, personally. It looks to me that the 800/1600 difference is just marketing, since they should have the same FSB since they use the same proc (and they haven't had upgraded cores like some Intel procs that are 400/533 FSB). And according to this tech doc,
http://www.amd.com/us-en/assets/cont...docs/24659.PDF , there is no difference.