For deer elk, antelope etc.. about 400 yards, longer than that and I need a range finder (other than the crosshairs). My hardest shot was around 375 yards from a kneeling position in a gusting wind, if it had been a calm day... who knows? the longest shot I've MADE was around 400-425 (I sitting using a snipersling) but I didn't kill the animal clean. Within 300 yards, we are having dinner.
For Prarie Dogs.. there is no limit to what I'll try. However, realisticly, from a heavier weapon on a bench etc.. maybe 450.. there is a whole lot of stuff happening (wind temperature humidity etc) at long range to vary the point of impact. I can't do it consistantly at that kind of range, but its fun to try.