Ok, I just went outside and measured mine for you. But in addition to the considerations you mentioned, you may need to also consider the type of king-pin the rig has. I'll explain that a bit more later.
Here's a photo of my 2013 Voltage 3200 sitting beside my house. As you might be able to see, it rests on a slight DOWN-slope... but the rig is level:
That said, here is the measurement from the king-pin. It's right at 43 ½ inches.
However... here is what I meant about the type of king-pin. Without trying to confuse you, I'll just say that Dutchmen provided different types of king-pins on Voltage models, depending on the various upgrade option packages the rig was built with. So your Voltage may have one similar to mine... or it may just be a standard one.
In any event, mine is equipped with an air-bag assisted king-pin box, which potentially makes the actual pin a bit lower than one without such a model.
I tried to get a decent photo of me holding the tape measure for you to see... but with only two hands, I couldn't get the correct angle. However, from the top of the king--pin box, to the bottom of the actual pin is right at 17 inches:
Hope this helps...