Yep...it doesn't cost them anything for you to run a 1/2 ton or to run it heavy, but may cost you in the long run in one way or another.
As has been said, you can do it and can do it safely, but you'll need to set it up the way you want for running expedite loads, add your own gear for however long you plan on being out, full your tank, and get it weighed at a local scale. Sometimes the guys that do metal scrap hauling will have a local scale if you dont want to hassle with the big truck scales.
That amount subtracted from the stated GVWR on your door label will result in your legal load limit. You might be able to safely haul a bit more and be comfortable with it, but realize the authorities will not see it as legal should you be stopped for any reason; accident, search (see the random search thread), etc.
Heavier than rated loads will also place undue stress on your 1500 and will inevitably cause it to fail prematurely in one way or another.
Like xiggi and Ragman have said, figure out the safe weight and then figure out what you will tell the outfits you run for as to your load limit.
You will still get asked if you want to take a load that's a couple hundred pounds or more too heavy and then you can decide if its worth it or not. Weather, road conditions, the shape you're in, distance, type of load, etc. You'll find too that your travel orders say one weight and when you get there it may be drastically different.
All up to you to be the one in control of what you take or not, and in control of being legal, and safe, or not.
I'll bet you'll find that once set up and loaded with personal gear you'll find you can't really haul as much as you might like. You'll still get loads, just not as many as someone who can safely haul a lot more.
Good luck man, let us know what you come up with and how you're doing.
And...Happy Thanksgiving!