I too have not made my way through the whole document yet...but a couple of my observations so far:
The congregated gifted programming under discussion does not appear to employ many of the strategies we often consider, such as curriculum compacting, acceleration, etc. The GCP students and the non GCP students had access to exactly the same curricula (the top-level bagrut, from what I can tell), and appear to have made fairly similar use of it. Based on the descriptions provided by the authors, in USA terms, the GCP students look more like a tracked AP cohort. I suspect that the actual difference between GCP and non-GCP was access to a community of peers, which appears to have been a very mild negative for the male students, and maybe a positive for the female students, if I'm reading this correctly.
The one substantive difference that the authors identify is greater breadth in the educational path of the GCP students, which I would consider of value not only to society, but also to the individual students. I know I am not alone among the adults on this forum who have delved into our own multipotentiality in ways that don't have obvious career outcomes, but have been personally satisfying.