GF-5/GF-6 additive levels will vary between brands. Formulas change periodically as well.
Oils more/less fall into these 3 buckets:
Oils w/o OEM or API approvals: Amsoil Signature Series, HPL, Redline, etc. Depending on who you talk to (and believe), these can be better or worse than mainstream oils containing OEM approvals.
Oils with OEM approvals and API licensing: vast majority of oils on the market, including some "generic" brands. For a given viscosity and performance spec, all of these oils will be very similar in performance. Their VOA's may look different, but the end performance should be very similar.
Oils w/OEM approvals and API licensing, but also advertise extended drain capabilities on their own: Mobil 1 EP, Castrol Edge EP, SuperTech 20K, etc. It seems reasonable to assume that these oils are more stout (to a degree), but that is also highly debatable.