Oh shoot, yes, silly me. I was thinking of a different post with DominiqueI personally do not link personality to breed, not as far as aggressive roosters go. Some of that is from my limited experience but most is from stories I read on here. You can read where roosters from Orpington, Delaware, Silkies, Barred Rocks, Rhode Island Reds, or about any other breeds have been absolute terrors or have been great. I don't judge whether a breed tends to go broody, how well they lay, when they start to lay, things like that based on one hen. I don't judge a breed's rooster behavior based on one rooster.
You never know how an immature cockerel will turn out when he grows up and is in charge. To me, juvenile behavior while hopped up on hormones isn't a great indicator of how he will behave when mature. If he is human aggressive he goes, no tolerance for that. But he may be fine with humans with humans as a cockered and change later. He may be really aggressive with the girls as a cockerel and become a total gentleman when he grows up. You just don't know.
If you have experience with your Orpington as a mature rooster and his behavior is OK, that would be a big plus for me.
Where did Dominiques come from? Maybe you saw that from another thread or maybe I just can't find it in this one? You are right, a Buff Orpington over a Dominique hen will give you a black sex link chick and you should be able to see the spot at hatch.
Delaware are also barred, you can see the barring in the black feathers, not the white. A Buff Orpington rooster over a Delaware hen will give you chicks where the boys will be barred and the girls will not but you can't see the spot at hatch. They have to feather out and you look at the black feathers. A Delaware rooster over Buff Orpington hens will not work this way. All his chicks will be barred when they feather out.