I can not find any snacks above a 6 for myth. The jar of jellybeans and the ambrose is only high level snacks i can find. I find level 7 snacks in other schools but not myth. I have to feed my myth pet Shanta Pudding to get any higher benefit from the snacks. If there is a higher myth snack in game other than buying the mega snacks please let me know.
Ok I don't suggest buying the snacks that you do now because they cost quite a bit. I think you should go to bazaar and buy delicious cookies, they sell for a cheap price usually about 200 gold or so. And if your pet is myth they will like the snack and get 6 points from it which is good or if they love it they will get 7. This way saves you money and will get your pet up pretty fast. I have around 11 epic pets and I have fed all of them glowing taffy, delicous cookie, spicy wings because they are all cheap. :P