I don't have a field computer.

I run drop sheets on Quicktarget, and sometimes JBM (JBM is a free online application)

http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

I typically run a table using 4500' el, 50F temp, and 25.50 Hg pressure, as that is about average around here.

I run a table at 10 yard intervals out to a mile or so. It takes a couple sheets of paper, but the data I need is there.

I also will put a simpler drop chart on the rifle stock, 20 yd increments, out to 700 yards or so for quick reference.

With these aids, it seems fairly easy to consistently hit 8" targets in field conditions out to 600 yards or so, and i'm being conservative. I'm shooting 308 and 30-06, mostly with a 208gr AMax at 2600-2750 fps depending on which rifle.

So with all that said, I'll throw 600 yards out as a reasonable range to make consistent hits on 8" targets, under good conditions.

The thing is, there are ALWAYS variables. Wind, temp, pressure, visibility, bullets, chamberings.

At the end of the day, have a reasonable chambering/bullet, a laser rangefinder, elevation turret, and practice, practice, practice.

I think you will find 600 yards becomes a very confident distance, and well beyond that distance, depending on your equipment, and personal skills/passion for it.