The Leupold rep told me that the Mark 4 has the same glass in it as the VX-III, which has been replaced by the VX-3. I asked if we would see a Mark 5 with the new VX-3 glass and he said no. According to the rep the only real improvement to the VX-3 was a different type of scracthcoating that was slightly better in low light conditions. Other than that, you would need lab equipment to be able to measure the slight increase in light transmission. If you can't afford a Mark 4 the discontinued VX-III (not vari-x III) can be had for some great deals. Downside being you would have to send it off for M1 knobs or mil dot reticle.
