Tires: Tire Pressure, scale weights, plackard

Question
OK here goes.  I have actual scale weights of my 2500 suburban loaded with all the "stuff" and passengers I carry around.  If I use the actual axle weights, and a service load and inflation table for my tires, it would indicate that I can carry 50 PSI on each tire with 900 lbs of carry capacity to "spare".This seems to conform to the front recommended pressure of 50PSI on the plackard.  BUT, my rear axle weight is actually lower that the front.  But the plackard calls for 80 psi. I am figuring that the manufacturer of my 2500 suburban has placarded the vehicle's recommended tire pressure to be safe carrying its maximum GVWR of 8,600lbs whereas my actual vehicle loaded weight is 7,200. Can I safely carry the 50PSI in the rear tires given these facts?  If not where is my thinking kinked?
Thanks,  

Answer
Dave,

There is much more involved in selecting a tire size and pressure than what is shown in the tables.  The recent Ford / Firestone has taught us that as you use less and less of the capacity of the tire, the rate of failure goes down.  What's interesting is that this is includes failures due to road hazards.  This also includes the tire's load capacity and its speed capability.

Plus, GM tested your vehicle at those pressure - both fully loaded and empty and has adjusted the springs, shocks, and sway bars so they perform in predictable ways at both conditions.  Changing the inflation pressure will change the spring rate of the tire (the damping rate, too, but that's much less important) and that will change how the vehicle responses in emergency manuevers.  

So I don't recommend deviating from the vehicle placard.