if you have a long commute, you dont want to run you tires at the max psi. like Grizzstang said, you will burn the middle of the tires out. you also have to think about expansion. if you have 50 psi in your tires and then you drive about 50-70 miles, you could have as much as 55 psi at the end of the run. if its hot outside, the problem gets worse. thats why i run mine low even when i am loaded down for a long trip. i went to Parker, AZ from Long Beach, CA and i managed about 20-21 MPG.
the best thing that you can do is pay attention to tire wear and check the pressure often.

 

The tire manufacturers allow for heat expansion when they list the max tire pressures. That is why it says max 50 psi cold. The OP asked what pressure he could safely run his tires at so he can safely inflate them to 50 psi cold. At least that is how it was explained to me when I worked as a tire jockey many years back. That being said I do the same thing as you in that I would never run a tire at it's max pressure. Even if I am fully loaded I would stay under the max pressure by a couple of pounds.

 

37 rear/ 35 front running light-40/40 at GVWR
Goodyear SR-A 235-15(whites in!) 40k only half worn!
Mine is a highway Jimmy,but has proved itself!
Never been stuck,but if the going gets tough,
the go pedal gets used! This is not an off road vehicle,
but it has never let me down with prudent caution either....

 

There should be a mfg decal on your door or pillar for suggested front and rear tire psi. (if your running factory size meats)

 

I would run 40 i run 40 in my blazer and get decent mileage