I'm just starting out. The cockerels we've processed were all less than 26 weeks, Turken mixes. They weren't as fat or meaty as the chickens you get at the grocery but they weren't designed to reach market weight in 9 weeks.
The taste is different. I haven't roasted one yet but we had tacos with dark meat and soup with the white. Both were very good. I made soup stock and it's fantastic. I'm going to brine and roast one this week.
Dorkings were meat birds in the past but not fast growers, they have a large breast on a short keel. Red Rangers are popular to raise in place of Cornish X for meat, are fast growers and have a smaller breast. The breeders goal is a large breasted fast growing bird with a longer keel. He also has Turkens in his flocks.
I have Turkens because they have less feathering, a huge plus for my climate and it means less plucking for the table. By Spring I should be able to make some decisions on keepers vs culls and process the different varieties.
Wiw, sorry for the novel!