@ what speed is this? I'm not finding that I build too fast. Any longer and I'd be bored sitting around waiting for my early scouts to take 30+ turns to train, or when trying to get an army out in Classic Age having to wait 6+ turns for each Elephant Rider in my Mounted XP and Production city (when wanting 10) is forever, 60+ turns before I can even start moving them towards my target, and that would be without any support units from the same city (then again I could build supports in other cities too... still 60+ turns though).
I think it's a matter of how one plays as well as what area one manages to get oneself into. Production city indicates a bunch of hills and/or jungles with a production resource or two in vicinity. Without that, for instance flatland start and no Copper/Iron/Lead for Forge, I'd probably "have" to rely on Mace-men, Axemen, Spear-men, Javelineers as anything bigger would take too long to train.
The reason for units to train faster in comparison to game speed is that you have less time to react to an opponent coming your way, if it's 10 turns advance warning you have in a faster game you can easily have 10+ units ready by the time he arrives. @Eternity it's more like 3 units, 4 if you're lucky, 5 if you're lucky and in a Golden Age, and that is as it is now. Double the time and you'd see 1 unit, 2 if you're lucky, and 2 if your lucky and in a Golden Age.
(As a footnote someone in Slavery can manage it a little faster but not everyone plays with Slavery, a manner of preference).
Now imagine the AI coping with these increased training times. An AI who can't react to an invading force on it's way and thus spends a lot more time building units to have as a buffer.
It'll suffer greatly and lose out faster yet in the tech race and expansion race as twice as many turns will go for building units it might or might not need. More if a smart player picks of a few straggling AI units here and there, forcing the AI to rebuild them time and time again.
So, I'm sorry but I feel that doubling, even increasing, unit building times in Eternity Speed will take away some of the fun of playing the game due to waiting time and reduced AI capacity.
Mind you I'm not saying the same for buildings. *grin*
Cheers