I have been reading for firm evidence in this matter and haven't found it.
Yes, by definition "proper air pressure will create proper contact which will create optimum traction." It's a tautological statement.
The issue at hand is: what is the proper air pressure for driving a 2WD Ranger with street tires in snow?"
I have not driven my 2WD Ranger in snow before. It's not new, but it's new to me. I don't know how it will react.
Here's an interesting read:
http://www.tirerack.com/winter/tech/techpage.jsp?techid=168
You are quite correct. Understanding and experiencing your Ranger in inclimate weather will make all the difference in the world. YOU have to make the decisions and asking for advice is the first step.
I grew up running back an forth across the Rockies and mid-west in 2wd everything, but mostly 1/2 ton pickups. They were almost always laden with a lot of heavy tools an ALWAYS ran snow tires in the winter. When you couldn't go any further we just stopped and put on chains. We ran across from Colorado Springs to Vail for work.
There are two things that will help you out in the Ranger. Put some weight in the bed and get some snow tires (preferably all four wheels). We run carbide steel studs in ours which makes a world of difference on the ice. The Firestone WinterForce tires are very good and less than $100 each. I remove the mags in November and put the steelies with snow tires (studded) on. We have (as most states do) laws that state you can only run studs for certain months, so they have to be swapped out by April 01.
One of the reasons that I like 4x4 is that when locked in, the front and rear wheels do exactly the same thing. You aren't pushing or pulling the wheels that don't have power applied. That means they go at the same time and at the same speed which means stability. The other thing they do is they all stop or brake at the same time, no pushing or pulling which means you have twice as many tires trying to stop you on uneven or slick surfaces because they are locked together.
The problem I have with automatics (in 2wd or 4x4 in 2wd) is that if you are attempting to stop; you may successfully stop the front tires, but the rear are still trying to push you. Now you can throw it into neutral if this happens, but I like the ability to disengage the engine from the drive train so that you aren't working against it when you try to stop. If you believe that this isn't so; try doing a power brake. Stand on your brakes and hit the gas. You'll either push the front tires or smoke the rears, your front wheels brake 80% of the load. I also like engine braking when in the mountains with a large load or trailer.