I know nothing of the SOP except for what I've heard about on this site. What I meant by separating SOP and dual purpose ( I should have said meat production) was that the birds would be too large for the SOP and not what they are intended to be. On the other hand a meat bird would be better growing faster.
"Standard" bred birds are often too large according to the Standard. There is a preference for the larger birds. That is common in some breeds.
The two breeds that you have showed the most interest in are medium large birds. They are not supposed to be too large and their advantage being reaching a 1940s-50s processing weight before their competitors, and not the final size that they get. In fact if they become too large, they lose some of that "competitive" advantage over their counterparts.
The Standard weight for the Delaware and New Hampshire is 8.5 lbs. Ideally you want your cock birds to be between a little over in the 9lb. range. Size is easy too lose and hard to get back, so you want to err on the heavier side. Not to any extreme though.
By comparison a Plymouth Rock's Standard weight is 9.5lbs and are commonly in the 11lb range.
Neither the New Hampshire nor the Delaware were meant to be "roasters". They were the start of the broiler industry where modern concepts of speed and efficiency was getting established. They were dressed out early as fryers, but now how we see fryers today. What was wanted was a meaty carcass at a young age that was at the peak of their growth curve. Somewhere in the neighborhood of 12 wks.
Over time their was some strains of New Hampshire that were developed to be larger, but the NH Cornish crosses were taking over, and eventually specialized strains of Cornish x White Rock. The New Hampshire accepted into the Standard are dual purpose birds. Back then there was high performing egg laying strains, and meat strains that was the breed New Hampshire. You cannot go too far to one side and not lose some of the other. The Standard New Hampshire is the bird in the middle.
Now, if you want to develop a specialized meat strain of New Hampshire, you can do that. It would not be the NH accepted into the Standard, but does not mean you cannot do it. It will require an outcross. You can still find New Hampshire influence in the colored broiler strains.