ChrisnAmanda1 - I can give you what I experience detecting here in Montana. I am located south of Missoula and have checked Missoula and the Bitterroot Valley towns a lot, and I have detected a bit in Great Falls, Simms, Polson, Kalispell, Whitefish, and several parts of Eastern Montana.
My detecting buddies have respectively a Nox 600 and a Nox 800, while I use the AT Pro. For the areas that we detect, semi arid climate, coins not really deep unless a yard has had turf brought in or extra fill dirt added, our finds are pretty equal. Similar amount of silvers, rings, wheaties, Indian head pennies etc. The NOX machines seem to pick up deep nickels better than my AT Pro, though I still get Liberty Heads and Buffalo Nickels too. For some reason I seem to find more silver coins but only because I thankfully get my coil over them, as all three machines would not miss them.
I bought my AT Pro before the Equinox line came out, and am totally satisfied with my Pro for detecting here in Montana. BUT... if I was thinking of hunting in different areas of the USA, especially like the WA & OREGON west side of the state, where the soil can be butter and the rains frequent, I would definitely purchase an Equinox! When I visit relatives in the Seattle area and I go detecting, I am CERTAIN that my AT Pro does not have enough depth capability to get to the older coins, as soft soil, vegetation buildup, and tons of moisture have moved those coins beyond what I can detect. I don't care much for the AT Max, I don't like the audio tones on that machine, and while it is a bit deeper than my Pro, I see no need for the Max here in Montana.
If you want to upgrade to a detector that will work ANYWHERE in the USA and give you good finds, I would definitely recommend either of the Equinox models. For hunting around Montana, Idaho, Wyoming and similar climates, the AT Pro or the Nox models would serve you well!