Highest payoff time for upgrades

Recently I saw SotL's video on the Paladin upgrade and just how much you need to invest for it to be worth it. However, therevare other upgrades which are even more expensive and haven't been covered. To my mind, these are SO, EWW, Torsion Engines and Logistica. What civs do you think have this payoff theme? This is not the same as late game strength, as pop efficiency also comes into play. What I want to know is how long would it take for a civ to make its upgrades worth it from a strictly cost efficient view.