They are very different. The V600 has 6 full cabins, 6 full en-suite heads, plus a queen-sized "pain cave." The V580 has 5 full cabins, 6 full heads (5 en-suite), and a queen-sized "pain cave."
So, you get a true extra cabin with the V600 - meaning all 12 guests can sleep in their own proper room. On the V580, if you want 12 guests somebody is getting the shaft (i.e. getting the "pain cave").
In addition, the V600 is a newer build, so you're going to get updated electronics and amenities. For example, the V600 Jus' Chillin has a 70gph watermaker, ice maker (which is more awesome than I thought it would be), 3-zone bluetooth-enabled audio system, full navionics suite including radar, etc.


The tender with the V600 is larger than a normal tender. However, if you're looking for the center-console 70hp tender that is an additional cost of $200/day.