With nothing coming close, the best I have ever used is the Leica Viper. We use them in the Air Force and would consistently range to over 6 miles easily. The coolest thing you can do with these is attach the mil GPS, range your target and it will give you the GPS coordinates of that target. It gives you the angle up or down and also the direction in Magnetic north towards your target. I ordered a pair for my section in 2003 and used to take them hunting to "stay proficient" with their use.
I remember them as part of the TACP Modernization and IIRC, they are $10K a pop.
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Part of acquisition contract were the Mark VIIs. Not sure of it range capabilities but a Mark VII is worth anywhere between $45,000 and $75,000.
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