Ho Hum - just to let yous all know that I've amended the SA v NA rating slightly. SA now only has one (1) plus v NA. I'm even tempted to give the plus to NA, but SA does get better radar coverage and sub launches from below Mexico.
However, the key to playing NA v SA is as follows: the majority of NA's population is concentrated in the north-east, and it's usual to bunch silos there just out of SA's radar range. SA's cities are all spread out and on the coast so not so easily defended with silos. Secondly, NA has the deployment advantage in the atlantic. Often, NA doesn't even bother deploying in the Pacific as California always dies anyway. So, by deploying entirely in the atlantic, NA can protect its silos and major cities from naval attack (they're hard to access from the Pacific, particularly if defended with airbases) and, most importantly, set up a line of battle parallel to the coast of Brazil. This makes besieging the SA coast much easier, especially if SA has concentrated most of his forces in the Pacific.
For a textbook example on how NA won this asymmetric contest, check out this recording
/looks to adjunct professor rimmer to continue tactical masterclass