The original question raised was what is the difference between the VX-6 and the VX6HD. This started when Nyrifleman (the person selling the VX-6) indicated for clarity this was not the HD model. Then, gte901m asked what was the difference between the two? So just comparing the VX6 to the VX6HD, the VX6HD upgrades include the Alumina® Flip-Back™ Lens Covers, upgraded lenses, CDS-ZL2 Elevation Dial, Zero-Lock windage dial, Electronic Reticle Level, and the Reversible Throw Lever.

Some will put value with part or all of the upgrades. Others may think the upgrades are not worth the increase in price.
Warpig602 was right, the VX5HD and VX3HD series have their own differences and do not share all the upgrades of the VX6HDs.

Still, not counting the upgrades, the VX-6 performs very close to the VX6HD to my eyes. I too believe you would have to have both scopes side by side to see if your eyes see any difference. From what others have observed, the difference, if you nit pick it to the nth degree, is in very low light, at the edge of the field of view, and at the highest magnifications.

donsm70 nailed it. The VX-6 is a great scope.

GLWYS