I'm looking for a scope for a new long range hunting rifle I'm having built. So, what's the big difference between the two? It looks like I can have knobs and a reticle added to the VX3 LR and it will be less expensive than the Mark 4 with same knobs and reticle. I want the M1 knobs and Mil-Dot reticle. Are the Mark 4's built better? Do they track more accurately? Any info would be great. Thanks in advance.