both premiere and alchemist od are software based. teranex is hardware based. all of them can do 4k framerate conversion.
as for transcoding, you'd have to be more specific what your needs are. adobe media encoder can encode to lots of formats and premiere now supports ingesting and exporting prores.
if you're doing a pure framerate conversion and not changing the speed of the video, then you don't need to worry about the sound as it can just be passed through unchanged which is what it sounds like you want, as you seem to put playback smoothness as your highest priority. As for motion artifacts, alchemist od and teranex do errors mapping so are higher quality in post, but, then again, premiere's framerate converter built in, is free.