Generally, slower speeds favour the human over the AI. Why?
1. As you point out, messing up something for individual turns doesn't have quite the same impact. Considering the AI messes up every turn anyway, for the AI it doesn't matter what speed it is

2. Military units of any particular era stay good for longer. A human player will put much more specific planning into a) beelining the required techs and b) setting up infrastructure/population/treasury to chop/whip/upgrade/buy/draft an army as fast as possible.
I think that will be my plan for Ragnar. I noticed that once you have Rifling, you can still build Berserkers. What's more, berserkers can be upgraded to rifles and retain the amphibious bonus. AND Ragnar is financial so teching to Rifling might not be so long, and then once there it shouldn't be a big stretch to save gold to upgrade berserkers to rifles. Plus, Rifles require more

than berserkers, something that is generally fairly scarce on archipelago maps.
Sure, you might miss out on earlier war opportunities by not using the berserkers straight away - but I'm aiming for space for this one, and letting the AI develop it's (my!) cities and land for an extra era might work in my favour.
My early game wishlist would be to nab both GLH and Collosus... maybe even Oracle for MC... and enough cities to make the GLH worth it... and workboats or galleys to explore... it's a pretty big wishlist. That list is kinda long, what to prioritise?
Hopefully Santa has something good for me. Time for me to get started and see if it actually works
