Short summary of the Byzantium game. I went for early Religion, which as usual for me included Desert Folklore, Tithe and Pagodas, with Messiah, and due to try for Cultural Vic: Cathedral. However, I was not the only one going for Cultural it seemed. After building up our small continent, me, England and Iroquois sat idle for some time. I stole two Workers from the English in early-game, thus keeping them down, but still managed to become Friends later. However, the Iroquois were constantly 'plotting against me', even though we were Friends. Luckily, I could position a couple of units between two mountains and stay safe (see screenshot).
I got both Hagia Sofia and Great Mosque and never had Wealth issues due to my Tithing. Thus, I got a number of CS Allies. My second city (Adrianople) had good Production in the desert and got Petra and certain other Wonders, but both England and some other Civ built Culture Wonders heavily, and Iroquois took a number of others. Actually, the English took both Uffizi and Louvre just ahead of me, to my chagrin! Beelining for Astronomy, I found out that Aztecs and Songhai (AGAIN) shared a smallish continent, while Netherlands (AGAIN) had one for itself and was clearly in Scientific lead. I went for heavy Religious spreading, particularly toward CS and Netherlands, and it paid off, as they clearly went for befriending me throughout the game. Finally, the Iroquois attacked me (while Friends), but I could easily stave them off from my fortified point. The Songhai joined me and took a Iroquois city on its continent, but I only defended. Later, the Netherlands asked me to join an assault on Iroquois and I saw my opportunity to wipe them from my continent and take their Wonders. It was quite an easy takeover with some GG cultural extensions and artilleries.
Then I got news of a Songhai fleet and army on its way toward Constantinople. So I quickly relocated all units toward my eastern borders and entered a Defensive Pact with the Netherlands. At the same time, England DOW'ed me, but it was easily staved off - I also had most of the CS as Allies, the remainder being Allied to my good Friend the Dutch. I had chosen the same Ideology as them (Order) to keep them on my side, and their cities were mostly following my Religion. The English were also wiped from my continent without much difficulty, mainly due to Landships and Submarines. The Songhai were wiped by the Aztecs and Dutch on the other one. While I could have taken the Cultural Victory in time, I just grabbed the Diplo as the opportunity presented itself - and I was tired of that game.
A couple of points I can present already. While I won with Byzantium, they were not at all helped by either their UA nor their UUs (in that game at least). Thus, until now, they've been the most difficult Civ to get ahead with. Also, particularly Songhai (cf. earlier games), but also Aztecs are not playing well as AIs, while the English (cf. earlier games) and the Iroqouis are playing quite well in early-to-mid game as AIs - especially in terms of Wonders. Below are some screenshots, one early, one mid (notice the easy mountain pass control towards the Iroquois), and two end turn ones.