According to the Brahma and Cochin Club of Austrialia website big medicine has the right prescription with regard to breeding darks and partridge (couldn't resist, sorry). They don't have anything to say about producing a true partridge color.Would be pure speculation on my part as well, but I think I would try to find a very good dark hen.
Mated to a partridge male, would produce gold based pullets, and split silver/gold cockerels. From there you could mate these gold pullets back to a partridge male to produce all gold chicks of both sexes.
Or if by chance one of the split males turns out to be the better typed bird, you could use him. Mated to a gold hen, would produce both silver and gold pullets, gold and split gold/silver cockerels.
Or you could breed this better typed split gold/silver male back to the original very good dark hen. This mating would produce pullets of both colors, silver and split cockerels, but hopefully of improved type.
Now something I'm unsure of, is whether proper partridge requires mahogany. I had assumed it did, and was the difference between a true partridge and the golden partridge prevalent in most Brahmas. If so, this would need to be aquired from another source, which will complicate things considerably. The beauty of the dark/partridge crossing being that they are the same pattern.
Here's a gold partridge pullet hatched on about 4/1/13 from a breeder kind enough to share some chicks with me from Iowa. I only have her, another pullet and a cockerel,
following a coyote attack this spring. Still kicking myself for letting that happen.