I think too many people concentrate on supplementing O3 in order to achieve the optimal balance when what would be healthier is working on bringing down your O6 consumption. Yes they need to be in balance but they BOTH need to be a low %age of your diet.
If you have already cut out the bad oils, that's most of the battle right there. Yes, grassfed does matter. If you are eating grassfed ruminants and some seafood, I don't see any need to supplement with O3.