My theory: When loading the megacivpack, it requires the enormous use of RAM. After it is loaded, next stress may be from randomness of picking civs if you are playing a game, not a scenario, unless you personally pick a civ. Next stress may come from randomly picking a civ for BarbCiv or Revolution option if you have both/either of them turned on. That is my theory anyway . Feel free to destroy that theory if it is mistaken in the name of better info .