Two environmental factors come into play that are often not discussed when picking a bag, altitude and humidity. If you have a trek that is relatively low in altitude and low humidity, then you may not need as warm a bag. Even after a rain at Philmont, the humidity is still relatively low compared with much of coastal America.
Altitude wise, there are a few treks that stay between 7000 - 9000 feet, and some that spend most of their time above 9000 feet. One factor is the temperature with respect to altitude. Every 1000 feet you climb, all else being equal, the temperature drops about 3.5 degrees. If your peak sleeping altitude is 11,700 feet, ie Phillips Camp, you'd likely be 10 degrees cooler than if your highest camp was at 8400 feet, Lower Sawmill. That should be taken into account in your equipment selection. A side effect of that is that at higher altitudes, the thinner air, even cold air, does not transmit cold (heat) as well as at sea level. If you have a bag that's great at freezing at sea level, it's probably keeps the heat out better at altitude.
Additionally, Philmont is pretty dry year round, even after it rains. Many people seem to sleep warmer in a dry climate for the same temperature than in a wet or high humidity climate.
Having said all that, I sleep comfortably *about* where *reputable* bag manufacturers rate their bags. I have a 20 F bag from Big Agnes. Even on top of Mt. Phillips Camp at the mid 20's, I had to sleep with the bag unzipped about 1/2 way, wearing a balaclava but not putting my head in the bag.
At base camp I was on top of the bag.
*Your Mileage May Vary.