I love playing long marathon single player games, mostly because I don't like my units going obsolete so quickly. That being said, if we play this game on Marathon we might still be playing when civ 6 comes out. I'm going to wait and see others thoughts on this, but as of right now I'm thinking normal would probably be the best, though if others think epic could be viable in terms of time I'd be willing to consider it. Playing on quick just makes the tech rate too quick for my tastes.