I shoot the majority of my video at 25fps, 50fps and, occasionally, 100fps, then after editing, render at 25fps.
I often intermix short sections of B roll from stock video which is often at 30fps and has no audio.
If I stretch the 30fps sections by the appropriate ratio (thus slowing it down slightly) so that it is processing 'frame by frame' is that likely to give me slightly better output quality for those sections?