Well now that I knew some of my units could go through borders and some could not, I gave a Tibet game a full try. Pushing for 5 cities is extremely easy, since you still get a few barbarian free kills with no barbarians attacking you, so the 2 cities to the north can be taken effortlessly. Grabbing the holy city first is vital. Then grab Pagan, and switch to scholasticism. It's easy to get 4 great prophets out of pataliputra before the Mughal respawn. The 30% Buddhism is a little tough, but after figuring out my missionaries can enter Independent cities as well, I had it done well before 1400AD. The last half of a Tibet game is unbelievably boring though, especially on Marathon. Basically what you have to do is turtle with Lhasa while building the last great prophet. So I spent a while just sitting there and spamming the space bar. I would have went on the conquest into India, but it seems none of my stronger units could go southward anymore due to jungles. Since I can't take anything with Khampas anymore, and a war with the Mongol Empire was just asking to be destroyed, I was forced to turtle.