At what distance do you need your rifle to be "effective?"
Unless you really train, the average shooter will be largely ineffective at non-predetermined distances beyond 300 yards, no matter what gun you give him.
If you are buying a dedicated target gun, to shoot at targets of known distance, the longer the barrel (within reason), and the heavier the overall gun (with virtually no limit), and the lighter the trigger, the more "effective" it will be at shooting groups that are "competitive" against the rest of the heavies on the line.
A lighter, shorter gun will be much more effective for other applications. The small loss of velocity will not be noticed by animate targets you are likely to encounter in the field.
A .308 at under 200 yards hits like a sledgehammer, no matter what you shoot it out of.