The RJF traits are strong in American Games. It is still common practice in Southeast Asia to cross the RJF into game birds, as it has been for a very long time, undoubtedly when game birds were obtained from Phoenician traders in Rome and spread throughout the Roman Empire, obtained by Spanish Galleons and transported throughout the Spanish Empire, obtained by Dutch traders and throughout the history of gamefowl, there is a high degree of RJF genes present. Those genes have been further selected for in that most games have been historically raised in a natural setting as semi feral birds. The selection went even further in their historical usage, as only the strongest, fastest, smartest and best males survived to pass their genes, mimicking nature in many ways.
Where they differ is the addition of malayoid, as opposed to bankivoid gamefowl genes. Although modern DNA study suggests a common ancestor for all chickens, many have believed that the malayoid (or shamoid) birds have a different wild ancestor, very much a true jungle fowl, just not the WRJF. They can survive in much the same wild setting, but are more apt to run than fly, are more adapted to grass than forest, have better night vision, have marrow filled bones, taller, more thickly built with more leg and less wing. They don't moult all at one time, and don't have the low testosterone period as the RJF does. They are more sparsely feathered, so winter survival is impacted in the more marginal junglefowl habitat that we see in the non tropical regions.
The true RJF will show eclipse plumage, white earlobes, and typically be a little smaller than a typical BBR standard gamefowl, either Spanish, American or Old English, all being basically the same bird, in many varieties besides BBR. The roundheads are showing a little more of the shamoid traits at face value, with their peacombs, but undoubtedly all games have a little of this influence, having been crossed on Asil with about the same frequency as they have been crossed with RJF throughout history.
The Peyton Democrat is one strain that comes to mind in American games that shows a white earlobe. Whether it comes from RJF or Leghorn is anyone's guess, as undoubtedly some gamefowl as well as some "wild" RJF have been influenced by the more modern breeds. It is usually frowned upon in the gamefowl community in general to see a white earlobe, in all but the rare exceptions when they are expected to have them, as it makes one think of leghorn, and the common thought is that a white ear lobed chicken lacks "gameness" and this could have been handed down in lore from the past when a white ear lobed chicken could be carrying too much RJF, and it would most likely appear to lack "gameness" in the low testosterone portion of the year. Conventional wisdom was to cross in asil to fix any lack of "gameness" , and this probably was owing to the shamoid trait of not having as pronounced of a breeding season.
Now the Fitzgerald chickens, I'm not so sure they couldn't have more AG influence than RJF influence. The pictures I have seen show a grey here and there, something you could expect with AG, but not with RJF. Survivability in the wild would probably be equal anywhere in North America, with AG probably having the edge, having been selected to survive and brood chicks in semi-feral conditions all the way to Canada. It was just the way they were raised, you had a sprawling estate, you raced horses and raised gamefowl. Or you were a dirt farmer in a shack with woods out back. In either case you had hens raising chicks with little intervention after being exposed to selected cocks, stags gathered in the fall and penned, pullets expected to survive as best they could, be that on scraps the hogs left or what the racehorses spilled out of their feeder. In some cases, the sprawling estate ran out of carrying capacity and the gentry farmed out some breeding stock to the poorer homestead type farmers. In most cases, the deal was that the homesteader raised the hens first brood out of the selected game cocks, the gentry got their pick of farm raised stags in the fall, and the farmer could use the hens to raise replacement egg layers on their subsequent broods and eat any extra stags or unwanted pullets. These were the days before electric incubators. Was not uncommon to find some game chickens on most any farm, regardless of whether anyone actually partook in any nefarious activities with them.