I remember having this issue when Civ V first launched. That the game seems to accelerate in tech, but production doesn't keep up. In my first playthrough, by the atomic(ish) era I'm getting techs faster than I can build a single unit. I remember this in Civ V too - before it was balanced a bit. This isn't just about pure speed, it's about relative speed, so I don't see why changing to 'epic' would help at all. Are other people seeing this?