Actually I was told by my Comcast guy, not saying this is true but this is what I was told, basically he said he plays on Xbox Live too and that the games are in fact played IN PART by a bigger server from Xbox or Microsoft. But he said that also the games will go off a HOSTS server as well so basically your connection (if you arent the host) shouldn’t matter very much or plays little to no part in your Xbox Live playing.
I have no idea about the PSN though, and this guy could be wrong but that’s what he said about it.