The iPhone 8 and 8 Plus have the same CPU and GPU as the iPhone X. The extra screen resolution (which is measured in PPI, not pixels) of the iPhone X is unnecessary IMHO unless you put the screen right up to your face like a retard, which means that it will only waste more cycles.
This means that games and other GPU-heavy apps could have a slight edge on the iPhone 8 followed by the 8 Plus.
And OLED screens, while being more vibrant when new, fade over time in ways that LCD screens don't.