When the 6+ was first released, I spent a few weeks here and there with one (passed around for development purposes), and I encountered a little stuttering on occasion, where it wasn't present at all on the 6 (or even earlier models for that matter). So most people assumed that scaling overhead was to blame.
As time has passed, the OS, apps and now [especially] the hardware
have gotten better - I'm a big stickler for this sort of thing, I hate owning something with a weird behavior you occasionally have to look over, so I passed on the original Plus, but I'm buying this iteration (pre-ordered at 2:59am, 64GB Space Gray

)because I'm 99.9% confident, it'll be a non-issue.