Not specific to Delawares, but this is a chart of historical market ages and weights for broilers. http://www.nationalchickencouncil.org/about-the-industry/statistics/u-s-broiler-performance/
The Chicken Of Tomorrow contest was in '48 - '49, and that's when stuff really started to change with meat birds.
That is a very interesting chart. 1985 until now is very interesting to me. The average to weight, live weight pounds, average days per pound, all take off.
What happened in 1985?