*nod*, the difference between normal and epic is that wars happen more completely within a single era, and you can build larger armies.
At epic speed (with 4 times as many turns):
Cities grow 4 times slower
Workers work 4 times slower
Cities build 4 times slower
Unless you insist on checking every screen every single turn, and micromanaging unit placement and exploration, the game doesn't go any slower.
During war, the game progresses at a slower pace, because you are manually moving your troops around. The effect is that your wars are more likely to end in the same era, and your standing army matters more. On quicker settings, you can often build an army to defend against attacking units before they reach you.
Interestingly, epic also makes slavery (and other rush abilities) more effective. You can use slavery 1 time per turn in both settings -- so in epic, you can build 4 units in the time it usually takes to whip 1 under the standard game. The "real cost" of slavery (population and unhappiness) isn't scaled down as much, so I guess that isn't all that important -- and the rate you can repeatedly whip production is usually only important when an army is moving at you, which scales up with your whip rate.
...
So really, epic isn't much slower.
A pseudo-marathon mod would be cute. Boost sight distance by a factor of 2, double unit movement, boost production speeds by 50%.
At epic speed (with 4 times as many turns):
Cities grow 4 times slower
Workers work 4 times slower
Cities build 4 times slower
Unless you insist on checking every screen every single turn, and micromanaging unit placement and exploration, the game doesn't go any slower.
During war, the game progresses at a slower pace, because you are manually moving your troops around. The effect is that your wars are more likely to end in the same era, and your standing army matters more. On quicker settings, you can often build an army to defend against attacking units before they reach you.
Interestingly, epic also makes slavery (and other rush abilities) more effective. You can use slavery 1 time per turn in both settings -- so in epic, you can build 4 units in the time it usually takes to whip 1 under the standard game. The "real cost" of slavery (population and unhappiness) isn't scaled down as much, so I guess that isn't all that important -- and the rate you can repeatedly whip production is usually only important when an army is moving at you, which scales up with your whip rate.
...
So really, epic isn't much slower.

A pseudo-marathon mod would be cute. Boost sight distance by a factor of 2, double unit movement, boost production speeds by 50%.