Most holdover reticles will not get you to 600yards without turning down the power.....Kinda defeats the perpose for me. Most will require you to taylor loads to it or adjust the power???? Kinda hard to keep track of things once you get a couple different setups. I pickt up a 4-14 Leupold that is hitting the road because its too limiting on yardages(does alright to 450 yards) and the little triangles just dont work for me.
Mildots are a good standard and depending on what power they calibrate the dot @ can be a great option.
My main hunting rifle is a 7mag with a 3-9 mildot scope. 9x is plenty for 600yards and in good conditions it does alright to 900yards.
The fixed power 16x IORs have ½mill hashes that work great in the field as the field of view is much larger than most scopes @ 16x.
The 6-24 IORs have the MP-8 reticles that are calibrated for mill @ 10x but @ 18x the hash marks then are MOA hashes wich with nost loads can get to 900 yards without dialing.