Ive got my Echo1 ASR sighted in at about 200 ft, and hitting accuratly at 250.
And personally, I would say that if your not getting out to 200ft, your not really effecting an advantage over an aeg. My wifes MP5 can hit the 100 - 120 ft mark pretty easyily. So to be a sniper and be effective, I would say that you have to hit 160 - 200 ft. Then you can hit without being heard, or seen right away.
Otherwise, the AEGs charge a quick couple of feet take cover and spray your position.