I do rocks, and have a manual trans, so I had some different parameters to work with. But maybe some of my thoughts can be helpful.
As already noted, if you aren't going to do much fourwheeling and don't think you need really low gears, maybe you don't need to spend the money on an Atlas. But if it's the right call for you...
One downside to gears that are too low with an auto trans is what was already mentioned, it might be too hard for the brakes to hold it back at idle. I don't have any direct experience with this so I won't go into it farther, but it's something to consider.
A downside to too low gear with any trans is if you need more wheel speed for mud, or sand or something. But one way to deal with that is to...
... consider the overlap (if any) between low range and high range. In my case (NV3550 / Atlas II with 4.30 low range):
- 4th gear - low range = 4.30:1
- 1st gear - high range = 4.01:1
- 5th gear - low range = 3.35:1
- 2nd gear - high range = 2.32:1
So there's just a little overlap between high and low and I can usually get by in whatever range I'm in. So if I'm mostly crawling slow I can usually go fast enough in 4th or 5th gear low range and don't need to stop and shift the transfer case. Or if I'm driving at higher speeds I usually can get by in 1st gear high range and don't need to stop to grab low range. Obviously if I had a 3.8:1 or 3:1 transfer case I'd have more overlap and I could more often just run in low range even if I would be going fast sometimes. But it would cost me low end obviously.
After having a 4.3:1 transfer case I've found that I LOVE it! Yes, I do rocks, so if you don't it might not be as big a deal. But I hit rocks with only 10% of the energy I used to. That's VERY noticeable in the seat-of-the-pants. And it's really nice to be ably to walk slowly up or down steep sections without having to give it a lot of gas or ride the brake.
So my advice would be to figure out how low you can go given the downsides of going too low, and then go as low as you can. I'm not saying 4.3:1 is the right answer for you. But if you're going with an Atlas I'd go lower rather than higher if you're on the fence.
