I think that most would agree that the "difficulty" of setups is related more to bird placement than simply the number of marks thrown. Factors such as wind, terrain, cover, and a dog's natural desire not to fight them all play into the "difficulty" of a setup. Factor in (no pun intended) retired guns (where the gunner is present when the mark is thrown and then disappears, forcing the dog to focus even more on where the mark is, due to a lack of reference from a white coat), and you add another element to your setup. And retiring the long marks is not always the most difficut. Many retrievers have problems "checking down" on short retired birds, causing them to drive through and get into trouble at other falls in the setup.
Triple with good bird placement beats a straight-up quad hands down Regards.
To get a better idea of what marking setups look like you can go to Working Retriever Central http://working-retriever.com/ and then go to the National Amatuer page. If you go to previous events they will have pictures and/or diagrams of the tests. There is also a brief overview of the fields performance on the tests. With a little searching you can also find these things for the National championships and both Canadian nationals.
Another factor is the breeding and training of our dogs over here. What is challenging for our dogs may or may not be challenging for dogs from other countries. And, vice versa. It also looks easier until you are standing at the line in front of the judges too!