Same glass in both but the VX-6 has a few more features like the internal level, illumination is standard, 6:1 zoom vs 5:1, ...If you never used a VX-6 You won't miss the bells & whistles...but I do enjoy a 3-18x verses 3-15x
The VX-5 3-15x44 can be had on gunbroker for $800
To me the glass is better than NXS, way better than a PST, better low light than Sightron S3(which by the way you should also be looking at). Waiting 6 months to get a Zeiss back made me quit them(HD5 issues).
Both the VX-5 & 6 are very compact and lightweight, I have several of the std & HD version and have had no tracking issues. Warranty issues will take forever with Zeiss, not as long with Swaro, Leupold is fast as they are in Oregon.
Leupold turret clicks feel a bit mushy compared to others but you get used to them.
Just my experience