Some applications using OpenGL or Vulkan and Wayland compositing end up with latency related to one or two frames of the screen refresh. Which means that characters appear onscreen much faster on a 144 or 240 Hz display.
Not really a surprise but something to be aware of.
That's just Evolution. It's a big, complicated turd that uses a thread pool with no priorities. So you can sit there waiting to read a message while it is blocked checking your other folders. Also it's keyboard shortcuts are stupid.
That used to be true back when the CPU did all of the GUI rendering. But now most all of it is offloaded to the GPU. Any GPU that can render Quake 3 Arena at 120 FPS (and that's ALL of them even Intel IGPs) can wiggle a window around very easily.
Not sure about file opens. Simple applications like GVIM don't seem to have seconds of delay for me, but I know what you mean with things like spreadsheet or word processor files. I guess it is all of the unzipping and XML processing.
Not really a surprise but something to be aware of.