The current numbers are stating that every 3.3 Det is equal to 1 Strength when it comes to how hard you hit, I believe. If you're looking to be a Tanky Tank, Det isn't vitally important unless you're not doing enough damage to hold threat against your party members.

If you're maximizing survival: Vit > Str > Parry > Det

If you're looking to deal a little extra damage: Vit > Str > Crit/Det > Parry

If you want to sacrifice mitigation for maximum damage: Str > Vit > Crit/Det > Parry

As for a precise amount of Det you want, there's no right answer for that. Just sacrifice whatever amount of Parry you're comfortable with losing for it if you want it higher.