I make sausage several times a week, mostly stuffed Kielbasa and smaller amounts of breakfast in bulk.
Over time I did some "People's Choice" testing and started with a 3/8" plate, went to a 1/4" plate for the second grind and finally settled on a 3/16" for the second grind as the majority like it the best.
The 3/16" plate does do a much better job of evenly distributing the fat on the second pass through, I still use a 3/8 or 10mm plate for the first grind.