If I can add my 2 cents... (note, I'm not playing with the latest SVN)
I've just made a test game on a large map, 6 or 8 civs starting, no rev and snail speed.
I've left the game autoplay for 4500 turns (almost 24 hours) and I've discovered the last tech. Since snail speed has 9900 turns, what am I supposed to do for the remaining 5400 turns?
I wonder, has ANYBODY every finished a game with C2C at snail or eternity speed?
From what I've seen in the xml speed file, Eternity, Snail, Marathon and Epic games are supposed to end in 3000AD (180.000 months); Normal speed is off-scale as it ends in 3060AD (if I'm not mistaken). Anyway the point is that with Snail speed, for example, I finish researching every tech well before half the turns I'm supposed to play. I guess NOBODY can really desire to play 5500 more turns without researching anything...
@Questdog, researching Priesthood in Jan 1943 isn't an eternity game: it's a game completely off scale. It's obvious there should be more turns before 1AD and less turns after; or better, turns should be completely reworked to at least try to match real world research. Researching Priesthood in 1943 is totally unacceptable: either we remove the year and leave only the turn indicator or I think we have to find a solution to this unrealistic year/research match.
One more thing: at snail speed, 95% of research with EVERY other rival civ being vassal to my civ (I have no more rivals so I have already won although I need to wait 5500 turn to reach victory...), I'm researching more than 400.000

per turn: nonetheless, I needed around 50 turns to research Euclidean 5-Space Geometry. Are you sure this is what you want when playing at snail speed (not to mention eternity...)?