The GVWR is usually the same on the last few years models. Nearest we all can tell, the GVWR is pretty artificial. But, the F450 Pickup model weighs more given heavier suspension and tires/wheels that give the F450 much larger diameter brakes. That leaves less weight for payload if you simply calculate GVWR-GVW. It’s not much though on similarly configured pickups. Last time I looked it was 200-300 lbs.
However, the F450 has higher rated rear tires and axle on most years. That along with the heavier suspension overall means will comfortably handle larger TCs and more payload than a F350 DRW.
There are also chassis model F350s and F450s. They typically have quite a bit higher GVWR. It seems most people are going with chassis models to haul the largest TCs.