The speedup is marginal and hardly perceivable. This theory Apple is slowing older phones to sell new models is simply untrue. On the other hand I challenge anyone to show me a perceivable difference between a 60 and 100Hz display. I think it just wastes energy. After all, if Apple didn’t waste that additional power budget from dropping a process node, then the device might last twice as long and battery aging wouldn’t be an incentive to buy a new phone anymore. Guess everyone missed that trick
Dupe: https://news.ycombinator.com/item?id=28291768
You can also just disable the battery performance optimization setting, but you could occasionally experience sudden loss of power with an old battery.