I keep and breed dark cornish as well. My dark cornish hens started laying before my black sex links did last Spring. I was really stunned. What I really like about the Cornish is they are very active and love to forage. They fly out of their enclosure every day to get in with the pigs and eat the leftovers. None of my sex links, RIRs or Rocks even consider it (my Sussex are very active too and do like to fly out and wander).
As far as volume, I think if you get decent quality animals, they will lay on par with any other purebred. Their eggs do tend towards medium size than jumbo. I've had two Cornish go broody already in their first year, so they are in the sensory depravation chamber for awhile. For some people, that is a good quality though.
Now, the White Laced Red Cornish have been bred for that particular color pattern. Therefore, they are more specialized than the dark or white cornish. My guess is they will lay less well than the dark cornish.
If I didn't mention it, I love my Cornish. Really cool critters that are very unique among chickens. They're like little bulldogs. I have a pen ready to do my first batch of homegrown Cornish Crosses right now. I'm very excited for that!
Oh, one more note, regarding sexing. The females will have smaller combs. BUT, beware, the females will also develop these really tiny spurs as well. Don't let this fool you. The males' spurs are much larger and rounder than the girls'.
I have no idea how to tell right now. They are 7 weeks old. If they are girls, will they lay very well?
