I've been noticing some stuttering on my 5. So far performance isn't as good as it was on 8.4. I hope there is still some indexing stuff going on in the background slowing the system down.
If someone asked me today "does is bring new life to old hardware" I'd have to say no. It's not as bad as what 4.0 did to the 3G but it is a noticeable slowdown. I can live with it but hopefully it'll get better.