"Smoothness" doesn't determine everything..if that was the case then a year old Mediatek chip can give you the smoothness if properly tweaked with software..but that doesn't mean its an optimum processor or better than the ones present today.
Software tweaking should always be a secondary thing..
SD615 as a processor compared to others in its kind has some thermal dissipation issues,much like SD810 ,due to which SD810 was abandoned by a lot of firms.