If it's loosely integrated (e.g. doesn't need super high bus access) it's not even as if it'll affect stuff like the clock tree or bus complexity much either.
I'd be surprised if the new CPU would take that much power, especially since for most use cases the CPU is mostly idle.
Was a pain to root, had to jump through a few hoops, but did manage to get Cyanogen on there. The result felt WAY better, snappy, better scrolling, much less aggressive at killing apps, faster app switching, minimal lag for the home button, and generally just a pleasure to use. I mentioned this in various forums and the theory was that Samsung was optimizing for benchmarks instead of multitasking. Even things like switching apps to use maps or contacts during a call would cause whatever app you were using to be killed. I returned the Samsung Note to stock before selling it, and checked, and sure enough it felt sluggish and even with just 2-3 apps going when I switched I'd get a splash screen as the app relaunched after being killed.
I "upgraded" to a pixel, that had less ram and CPU, and it felt WAY better than the stock Samsung Note. I do wonder if your results are related to the Samsung software being optimized for benchmarks (i.e. running the clock high, killing off anything that's not fullscreen currently, etc) instead of interactive use. Generally the OnePlus phones seem to be closer to pure android than Samsung from what I can tell.