The range highly depends on what you are looking to decern. You didn't say what the primary use would need to work on so I'll just say my experience with the Lieca 10x40's and Leupold 12-40 spotter has been.
Impacts on white painted steel plates;
10x binos - 500-500 yds
40x spotter - 1000 yds no problem.
Paper Targets - in the white;
10x binos - 300 yds
40x spotter - 500 - 600 yds
Paper Targets - in the black;
10x binos - 100 yds
40x spotter - 200 - 300 yds
Small points (presence and or length and or location) on a moose antler;
10x binos - 200 - 500 yds
40x spotter - 500 - 1500 yds
Spotting moose is in general is highly subjective and depends on cover, shade, movement etc.
10x binos - 0 - 500+ yds, maybe miles just depending.
40x spotter - 500 - 2000 yds, maybe miles too.
All ranges are subject to conditions and can vary, especially if you use a tripod with the binos. Ranges are just best guesses from memory. I was shooting the other day and couldn't see the hits on the target that were in the blue at 200 yards with the NF on 22x, barely could with the Lupy on 40x! I been making up my own targets on index cards with 1/8th" black lined diamonds 2" point to point because of that. They punch perfect holes and easy to see, choose your flourescent color.
[ 04-01-2003: Message edited by: Brent ]