One thing about Gavelkind is that it doesn't split up counties, so if you own every single holding in your capital country then your primary heir will inherit them all, even if it means some of his brothers end up landless.
This gives you a strong and compact power base, but of course less taxes than spreading your demesne across many counties, since you wont have many mayor vassals. As a bonus each holding in the county can benefit from the marshal's levy buffing mission, giving a significant boost to your personal army size.
With the Old Gods coming up it seems like it's time to get used to gavelkind
-Spectacle