For the purposes of my last post: where a 240gr fired at 1100 fps is ballistically ineffective.
This is actually closer than what I would consider mid-range with a full-power .308.
If I had to draw lines, I'd say short range is 0-300, mid 300-600, long 600-1000. But that's pretty much arbitrary based on some different factors.
If you're thinking about a mid/long-range rifle and the suppressor is incidental, it's no different than picking a good LR rifle.
If you want something as quiet as possible, your max realistic engagement range is limited dramatically. A .300 fireball shooting a 240gr SMK at 1100 fps will have as much drop at 300 yards that a regular .308 has at 1000. At 300 yards, it's dropping roughly one inch per yard.
If you want a demo of any of this stuff we can probably arrange it.