Just finished an Immortal/Pangea/Standard/Non-legendary OCC game as Ramesses. It got pretty tight at the end when both Germany and Russia DoWed me a few turns before my final policy. I didn't have the best defensive position (a few hills one side, grass the other) but managed to hold them off until I completed the Utopia project. My city was down to about 10 health and my only remaining combat unit was an artilery piece in the city! Perhaps could have held out another few turns as there were no units about at the end.
One of the things that saved me was my citadels. I'd set up three on scattered hills around my city, and, with a fortified mech infantry on each they don't fall easy! Swarms of panzers and mech inf would fly in and mostly die to arty and citadel goodness. I lost them eventually, but I was easily getting 20:1 kill ratios by just sitting there. I was also heavily helped by a bug which gave me a Khan from a city state... +4 healing per turn beats +2 by a long way!
Fortunetly I had marble to start, and, with the tradtion boost as well I could chuck out wonders like anything. Managed to get stonehenge (really helps!) and the oracle (also really helps). Maritime city states were useful, but I found I ran very short on cash around the industrial era. Unit maintainance was my main problem and at times I was running a deficit, living off the three luxury sales I managed to snare in my 4 tile radius, and open borders to far away AIs.
The trees I ended up with were Tradition, Piety, Patronage, Freedom and Order. I think Tradition, Piety, Patronage and Freedom are pretty much must-haves for an OCC cultural win. Tradition for the combat bonus and wonders, patronage 'cos of awesome, Piety because it has two free SPs in it and Freedom because it really helps culture and reduces SP cost.
The 5th is harder to pick, and I think I should have gone commerce with hindsight. +25% gold as an initial take allows for one point earlyish, before filling it up with the mostly useless ones at the end. Order's main bonus is the +5 production (ok, but comes late) and the +25% attack in own land (I was defending most of the time!).
Another thing worth bearing in mind is that unhappiness rarely comes into effect, and the only real benifit you get from it is a little bit of culture (from Piety) and occasional golden ages (I got 3). I was pretty constantly over 10 happiness, even while selling all my luxuries. Mostly from CS luxuries though - I never built any happiness buildings.
