Aye, when I say mine get plenty to forage, I mean lots of bramble, bracken, roots etc etc.
And like Karen says, I really don't think a couple of % on the protein levels makes that much difference, unless you are doing it indoors, with fast growing, high feed converting piggies who you need to try to finish quick.
I'm really interested in the feeding amounts though, as its what I always hear on here, lb a a day per month up till 5 months. . . . . but my growers never get beyond 3.5 lbs a day, and the adult sows get about 4-6lb a day depending on what they are doing (i.e pre farrowing, pre mating, etc etc).