24 weeks is excellent. I would take that in a heart beat. Combine that with preserving my existing meat qualities and that would be a real winner. I'll be paying close attention this year, regarding an acceptable fryer size. I know they make good roasters. Realistically, I would not be dissapointed with 20 weeks. I think you have stated that your NH's achieve 4 lbs dressed at 16 weeks. That is very good.
24 wks. for Hens that get to be 7lbs is good. That is also early enough to have a April hatched bird laying by the 1st of October. A March hatched bird in September. Long before the days get so short that they wait until the Spring. LOL. We need the pullets fully in lay before the days get too short in order for them to be reasonable winter layers.
You would have to outcross to something that good or better to get there in this lifetime though. It does require real choices.
Believe it or not, those in the picture were crossed with Delaware, and then repeatedly bred back to Barred Rocks.