I appreciate your input, but I came to this value after extensive surveying and testing to see what potency efficiency module lvl 4 would need to be at all considered for postgame builds. The answer is that it needs a lot.
This is for two reasons. First, by the time you have efficiency lvl 3, you already have a very stable power situation and pollution-defense situation. Second, you can already achieve -80% power limit on all machines with lvl 2 eff modules, so the higher tier eff module solely counteracts the debuffs of other modules.
Speed or prod modules can be spammed liberally and blindly in mid-postgame situations to maximize production, so eff-4 modules really need to go hard to justify the opportunity cost of not using a speed/prod module. Players were simply not willing to use eff-4 modules even at -80% power reduction with no speed penalty (which was my first prototype). The value proposition is also very sensitive to any speed penalty, due to that opportunity cost. This is not like a speed 4 module, where even a modest upgrade for +60% speed has widespread effects across every single machine and setup in your save file.
