I would say that they are progressing nicely. Cochins in general, especially large fowl Cochins are one of the slowest developing breeds. They go through a very awkward and gangly (sp) stage where they are building the bone structure and then they fill in the muscle and feathers. They look to be right on track for a 4 month old LF Cochin. Partridge appear to be smaller, but most of the Partridge LF that you find in the U.S. are smaller framed birds. There are a few breeders working to correct that and you'll find that their Partridge Cochins are larger.
The real test in the quality of what you've raised or bred is to see what they look like at the 2 year mark after they've gone through a breeding season and molted in again. If at that point the bird hasn't fallen apart and is a good representative of the breed, then you have a valuable breeder bird. I've seen plenty of ckls and pullets that look great as yearlings, but are a disappointment as a 2 year old bird. Some breeders will not use pullets and cockerels in their breeding pens for this very reason.