I bought 3 large boxes of Persil Bio powder months ago, and still have about 1-1/2 boxes left. It is my favorite detergent. I use it for large loads of very stained kitchen whites, coupled with the Sanitize cycle on my Frigidaire 4474 front-loader.
The Sanitize cycle provides a great "profile" wash, with the water being gradually heated to 152 degrees. I add liquid chlorine bleach (which is injected into the first rinse) and haven't found a stain that this combination can't remove.
I find that Persil powder rinses out much more cleanly than US Tide products, which clean well, but have tenacious suds.