Transducer power

[rolmops]

I just read some posts by people who bought a Furuno 585 or 587 with the 600 w or 1000 w capacity. The advice given in that post was to use a 600 w transducer instead of a 1kw transducer. It is my understanding that by using the 600 watt setup, you just as well might have either kept the Furuno 582 or the 620 /627 which are built with a 600 watt capacity. So why choose a 585/587 ? what other improvements does it have over the 620/627?