I used Sweet and Sour Eel + Miso-Glazed Cod and battled Rockgagong until they both cooked, then escaped and did it again. Capacity went up 9-11 points every time up to 9000, then it went up 4-6 points.
When I wasn't doing that, I used Miso Stew the rest of the time.
And yes, using the +500 grade shop bonus and carrying over the eleth mixer is a good idea, that's what I did.
Won't change until FPS's are no longer popular 9/12/10