I can vouch for the egg laying work ethic of SL Wyandottes;. The birds I had from Herb Holtz stock churned out eggs , came into lay at 5-6 months, and made large birds with good carcasses.When reading the question asked about egg laying in Heritage breeds, I was reminded about a contest I had read about in the APA book I have for the LF Wyandotte.
As the story goes, during a very cold winter in 1899 my friend was getting a wonderful egg yield. I supposed that he had a comfortable pen and was giving them the best of care. One day I went to see his birds and was amazed to find them housed in nothing more than an open shed and getting hard grain twice a day. This setting me thinking because he was getting far better results than I was getting from my Rock pullets, with double the care. The next year I purchased several settings of White Wyandotte eggs and hatched chicks in the latter part of May and middle of June. I had 20 Wyandotte pullets and 40 Rock pullets hatched in May. Both lots had equal care but the Wyandotte pullets out laid the Rock pullets two to one. The Wyandotte excels as a winter layer and the Leghorn as a summer layer.
A five year egg laying contest was done at MO. State Poultry Experiment Station:
1st place - White Wyandotte
2nd place - SLW
3rd place - SC White Leghorn
4th place - SC Reds
5th place - Black Minorcas
6th place - RC Reds
7th place - Anconas
8th place - Barred Rock
9th place - White Orpington
My personal experience is that all of my LF Wyandottes are great layers all year round. I am always reading in the winter that no one is getting eggs without supplementing extra light, no extra light here and all are laying every day here. In the Summer people complain their birds are not laying....still laying here, they only slow down a bit if going through a hard molt, but most all of them keep laying.
I have been pleasantly surprised at how my English x American Buff Orps have performed. They come into lay at almost exactly 5 months, and stay at it, most times laying right through their molt.. Excess cockerels dress out at 5-5 1/2 lbs at 5-6 months also, with plenty of breast meat. Hens weigh out at 9-10 lbs at a year, and are truly a roasting bird, fit to feed a family Sunday dinner.
I've found that to get this growth and performance it is important to feed the growing chicks very well, and be religious about treating for parasites in my climate, but it is so worth it in the long run.Once laying, the birds are easy keepers, who spend a lot of time ranging.