Re: VXIII vs VX3
Whatever you do don't get a Mark 4 - be sure and get a Mk.IV. They go to 11.
The first one you list is known as the "Vee-Ex eye-eye-eye". They were a special run for the Navy. The VX3 is made for people that can't understand the Greek numbering system and are priced accordingly. It comes with a decoder ring in the box should you need to convert decimal to Greek notation, kinda like a mil-dot master only better.
Just kidding.
They are the same, just different nomenclature representation for the same line from Lupy. I think you mean Vari-X versus VX - that denotes a change in the Lupy product line.
What is most important is the specific model number of the scope so you know you are comparing apples to apples for the same scope and the only difference is the price.