If you are using the rifle as a walking varminter, balance is more important than it is if you are shooting solely from the bench or from bi-pod prone. The barrel length in that case should be determined by the weight of the barrel and its effect on the over all balance and handling characteristics of the rifle. Having said that, a sporter barrel 22"-24" in length usually results in a nice handling rifle. A heavier contour barrel will produce a similar balance at 20".
Its generally accepted that a shorter barrel is stiffer, and that a stiff barrel produces better accuracy then a whippy one. The question then is, can you make use of the difference in real world shooting or is the difference theoretical? Again, that depends on how the rifle will be used. From a sandbagged rest at a paper target, you should be able to detect tighter groups from a stiffer barrel (all things being equal) but if shooting from field positions at live targets, don't count on it.
Then we have concerns about flatness of trajectory and wind drift as a result of choosing a shorter barrel. Trajectory is a non issue, if you have to add an extra click or two of elevation to your scope, its not like you have the other barrel there for comparison, so it makes no difference, provided you have enough elevation adjustment in your scope for the range at which you're shooting. Compensating for wind drift is less precise and matters even less. A stiff full value Churchill cross wind will drift a 52 gr bullet from a .223 about a foot at 100 yards and a 100 fps either way doesn't change that much. If you want to shoot in windy conditions, select a bullet with a higher BC if your twist will handle it, otherwise reposition to make the shot.
