Exactly correct. The least taxing is the x2 HiDPI 1152x720, or the "larger text" option in display settings. Everything else that is available as an option in display settings (and those up to around 1680x1050 using third party apps) will be more taxing, but ultimately to a nearly identical degree, and not something that will be readily apparent or even noticeable for the most part. This is because the "off screen" scaling calculations aren't significant enough to make much of a difference. (the super high res calculations aren't actually "drawn", hence the term "off screen." So, unlike what a lot of people here seem to believe, these higher resolutions aren't "pushing" 4K UHD pixels at a scaled resolution of 1920x1200 for example.) It is only when you start actually drawing those higher number of pixels on a larger external display that you start to see proper, noticeable degradation in performance.
A lot of these are placebo effect it seems like. People expect it to perform less, so they see it.