I've been playing 1.74b5 for a bit now, and discovered a few things out of the ordinary.
The game is Giant map (PW2), Prince difficulty, Epic speed.
1)I'm now in 1930 and just about done researching Physics. I thought at first maybe it's just a fluke and I was being rubbish, but as I looked closer, it dawned on me that while I was playing on Epic speed, turn increments were still 5 years. I know you've changed settings for Epic speed amongst others, so I had a look in Civ4GameSpeedInfo.xml, to check.
First off, it seems that it should change from 5 year increments to 4 year increments in 625 AD, which it obviously hasn't. Furthermore, it seems with the current definitions, the game will end in... 2281.25. This seems somewhat off. I checked the SVN trunk to see if it was a fluke, but it's the same in the current revision. I'm quite puzzled, because not only does the XML definition not add up to standard game years, but the game doesn't even seem to follow the definitions. This one's very puzzling.
The timeline seemed very, very, very accurate up until the medieval period around 650-750. That might well coincide with it "forgetting" to make turn increments shorter around that time. Unfortunately I took a massive stint from 260 AD to 1560 AD so I have no intermediate savegames to check on date increments.
Update: I set it to autoplay, and in 2000 AD it changed to 4 year turn increments.
2) About guilds, I've noticed my log saying they've randomly been founded, often in my cities, while I have done no such thing. Nor have I built the prerequisite(s), much less had a Great Person to inaugurate it. I can however build Guild Masters, but they can't actually spread the guild. Check the Master Clerk stationed in Toulouse in the attached savegame.
3)I'd turned off Flexible Difficulty, but I kept getting info in my log saying "Difficulty increased". Apparently I've been playing on Deity for most of the game, but it honestly doesn't feel that way. RoM Options says Flexible Difficulty is however enabled. Not entirely sure what to make of it.
Other than that, it feels very smooth and I was especially impressed with how well the game followed the timeline, up until said point. The amount of different buildings never feels too overwhelming on slower speeds and it just feels like the best incarnation of Civ4 so far.