So FLIR gives a bunch of numbers about "detection" which are kinda BS. Are you familiar with rangefinders? How your Bushnell Scout will do "1000 yards" on the box but only 250 yards to a deer? Its kindof like that but not quite as bad.
There are two things that determine how far you can see: the size of your detector and the size of your lens. So units with a longer lens will get you closer, and units with a bigger detector will be more sensitive.
Using the more common ones, like the PS32, I think I'd be confident picking up a coyote at 250 yards. But for the further stuff I would be tempted to use a BTS-XR like I have in the video. That unit is larger, but it has a 640X480 detector and you can swap the lenses on it. The 35mm lens is what you see in the video, but a 100mm lens would be more like a ten or twelve power binocular.
Personally I'm waiting for the LS64 to get here. Its a 640x512 detector in the same package as the little PS units. Its got a 35mm lens built in, and then a 1-4X internal zoom.