Have done a lot (LOT) of ransacking/potion making/alchemy and have maxed all those 3 skills, and have got a bunch of toons up to ransacking level 12 or 13 as well along the way. It seems as though you have more success getting the finest items from the lowest mobs once you get past ransacking level 12.
So, farm the lowest mobs that give finest items if that is your target.
Just my perspective. You may or may not agree.
PS: It takes about 850 cooks to go from level 9 to level 10 Cooking. Happy trails.