Need answers to parallax adjustment vs preset

While hunting we find in many instances there is not time to fart around with adjusting scope parallax and lots of those situations occur from 10 yards to 50 or 60 yards. My question is with two exact scopes one with parallax adjustment and one preset at 100 yards both set at 6X FFP, what is the point of impact difference in inches, mm, moa or mils? Again what I'm curious about is finding if there is an appreciable (I'm gonna miss) difference. Lets use a standard .22 caliber with 18.1 JSB at 870 to 910 fps as the sample.

Thanks Nick
 
With some of my scopes, at 50 yards, with the parallax out of adjustment, the point of aim can change several inches at the extremes of the eyebox. Normally we do a decent job of centering our eye, and thus we normally don't experience several inches. The amount of parallax error is related to, how well centered you are on the eyebox, and how repeatable your cheek weld is.