Noble difficulty is too hard. Tried twice....the first time I fell hopelessly behind everyone else even with most of a continent to myself, the second time I went culture-heavy but still managed to get squeezed on usable land by my neighbors. Tried attacking them at key points to gain more maneuvering room with limited success; but then my captured cities started rebelling. Geez, such ingratitude.
Well, if you expand too quickly, you'll fall behind technologically because your economy can't support it. If you build only culture, you'll not be able to defend yourself. If you have culture and a decent amount of units in a city, they shouldn't be rebelling. I'd suggest building up a core group of cities, build a big army, take more cities, and then hold them.
Sadly, I can't win any kind of peaceful game. I'm only successful as a warmonger.