I like that your reporting the layers too. It keeps everything in perspective. Your going to find the Jersey Giants are very slow to mature. Gargantuan birds typically are. Surprisingly enough your dual purpose birds that only reach 7lbs adult weight are faster to gain weight at younger age than much larger breeds. Look at the Buckeye and New Hampshire for good examples of this the on the other extreme you've got the Jersey Giant and Brahma types that are slow and steady.
I hope you keep up with the reporting. Dates of weigh in and average weights are great. At 6 weeks the largest birds, both largest pullet and largest cockerel, will be you prime candidates for future breeding. The Buckeye conservation reports confirm that your fastest maturing, largest at young age, are those from 6 weeks on. Also those birds are likely not to be your largest one year old birds. There is folly to breeders only using largest adult cocks. Sure the final bird is large but why would you want that much stew quality meat? Lose a 1/2 pound or more in final weight yet gaining more weight at grill, fryer and roaster age is a much better trade off in my mind.