JG in my opinion is not something I would use to make a DP. I tried it and I used several DP hens (Delaware, Barred Rock, RIR) The Cockerels took forever to get meaty. JG grow their frames the first year and then grow meat the second. Crossing them with another breed doesn't change that fact. I actually rehomed my JG that I absolutely loved, but he was destroying my girls backs, my Deathlayers do not do that. I would love to get JG females though, but I will never go down the roo path with JG again.
The grow out for JG cross is well past 20 weeks. I have 22 week old cockerels that still don't look meaty, but if I wait any longer they will be too old for the cooking method we use.
The best DP cross we have butchered was the Easter Egger cross. We got it from someone at a swap and it ended up being a cockerel. It was nice and meaty, it had very nice meaty breasts.
Orpington cross was my least favorite. Way too much feathers and was just a pain to butcher overall.
Right now I am working on Deathlayer cross DP. So far I think Squatch (JG) is still in my flock and it is driving me crazy. I am going to set some more eggs this weekend to see if he is out of the mix. He has been gone for about 4ish weeks so let's hope his DNA is gone because I am over all these black chicks.
And if you're plucking... You want WHITE to be the most dominant feather color or something that isn't black. Black feathered birds do not pluck well. It makes a very sad looking carcass because you can never fully make them look extremely clean. My black feathered birds are always skinned.