I have talked to 3 different people at leupold about this..According to them the only difference in the vx-3 and the MK4 is the MK4 has alittle thicker housing and a more durable coating on the Lenses. That being said I am hung between just buying a VX3 6-20x50 and having it sent in for M1 knobs or getting the MK4. Price wise there is about $225 diffence. That is not alot but that would allow me enough to get the VX3 4-14x50 I want to put on my hunting rifle also..What would you guys do..I've been worried/thinking about this for going on 2 weeks now..I can't make up my mind..Another think I'm considering is resale value if I ever decide to go a different route..