I still think that there's something fishy going on with adaptivity and render selected combo. I reported it on mantis with earlier build, but i was told that it's expected and report was closed. I'll try one more time to report it here.
Build RC2
When adaptivity is on and render selected is active, rendering time and amount of passes highly depends on "background" in VFB i.e. on what's not being selected and should not render. I'm attaching three renders. In all of them only column object is being rendered as render selected. The only difference is "background" - empty, low quality and high quality. As you can see from render stamp, render times and amount of passes differs wildly, as well as visible noise level on column object. Rendering was stopped by noise level limit - 5. No denoising involved.
I also did quick test with render selected but without adaptivity and in that case, "background" didn't do any difference.