I am not the most experienced pig-rearer on here, but I'll share my experience.
I have been told to halve the feed in the last fortnight and that you can take up to 1cm of fat off by doing this. I do usually cut down a little for the last two weeks and I do think I can see a difference. However, with free range pigs, being a softie, I wouldn't cut the food by much when the weather has just turned colder!
I haven't ever fed any of my traditional-type pigs as much as 6lbs hard feed a day, not even in winter; most seem to be getting plenty with 4lbs, perhaps 5lbs for bigger, fast-growing types like Saddlebacks, or in the depths of winter.
So my regime is up to 4lbs/pig/day, higher protein up to 4 months then onto a sow roll / lower protein but staying on 4lbs. Fresh veg etc when available, and free-ranging with roots and stuff to go at. Cut down by 1lb/pig/day for the last couple of weeks but make sure they have plenty of straw to play with / keep them warm.
That said, my Large Blacks I did find to be very slow-growing, and they maybe would have grown faster with more of a higher protein ration for longer. They did not have such good conformation - less eye in the bacon, etc - as some of the other breeds but oh my goodness the flavour more than compensates.
The best sausages we've had from any of our pigs, and the butcher swears he made them the same as he always does.