Both the brands you mentioned are very good and well priced. 600/WS should be minimum. You can buy Bron Color if you have an unlimited budget.

By the way, to shoot food properly you need to use mostly back lighting and only a very very light fill from the front to cover some of the shadows.So about 3 lights. Usually you would put grids/honey combs on the back lights to bring out nice hard detail and texture on the food. Grids will suck up 2 stops of light on average. That means 2 stops of light will be lost from the use of grids normally. So 400/WS quickly becomes almost useless for food. Also these small 400/WS Elinchrom heads I don't think are designed to use with many of their standard light shaping attachments like grids, so that might be a problem. I hope that helps.