I think the
N95-3 is more of a re-make, an improvement.
Review: Nokia N95-3 aka N95 North America aka N95 US 3G aka the New N95 at the Nokia blog
The 8gb is a different again, bigger screen, no memory slot.
Nokia N95 8GB - Mobile Gazette - Mobile Phone News
Could be wrong, but that's my understanding. Make sure you know which one you are after. ;)