Based on the observation that Roku video output is always* 60Hz, if you are going to single frame rate, it better be 30/29.97 - since for 24fps the player does 3:2 pulldown (or worse) anyway. Out of curiosity, how does Roku perform currently on your VFR videos?
(*) see
pending question. Also rumor has it legacy (fw3) Roku players could've output in native 24fps.