You are correct for "standard" routes, or trips where the fuel load is such that there is no effective payload limit. However, the 744 reaches the max payload well before the main deck is full on these max-fuel trips.
FedEx and UPS and DHL are apparently trying to one-up each other with these long-range nonstop routes. FedEx even has a video published that compares their 777 to a UPS 744 on the PVG-MEM/SDF run: