That's an interesting perspective. I have only raised a few BBW (3 to be exact), so I am no expert here, but my take would have been that since they are such efficient converters of feed they could get by on lower protein sooner than heritage birds. I have a friend who raises two BB a year for the holidays, and he only uses meat maker feed, even for starting.
As I'm sure you've read on this site, some people keep heritage birds on starter forever, and some drop the starter much sooner. I try to switch at 6 weeks when I move from the brooder to the fields. This year we had a very late spring followed by record heat, and I have birds of different ages. The younger birds didn't seem to be keeping pace with the older ones for growth, so I have temporarily blended back to about 25% protein.
Around here, the starter cost about 20% more than the grower. There is no way the birds get 20% larger, or attain maximum weight 20% sooner if left on the starter. So there must be an economically determinable maximum turkey per dollar switching point. However, also to consider are nutritional risks associated with insufficient protein. By free-ranging, my birds are able to eat different amounts of grass, bugs, and feed to self-adjust their diet. If your birds are penned up and only get feed, you may not be able to switch them off the starter as soon as I do. And its quite possible that my birds might get a little larger if I offered them the higher protein longer. On second thought, maybe I don't want them larger. Most of my customers don't want the really big birds anyway. They all seem to want birds that dress out at either 15 lb or 10 lb. The tom Bourbon Reds and Standard Bronzes are the hardest to sell because they're too big!
