M4 airsoft accuracy and fps?

i need a short m4 AEG. i'm not sure what the shortest m4 is. i need the shortest m4 (except the stubby killer) that can reach up to 480 fps and still be very accurate.. does tighter barrel mean more accurate? some say longer barrel is more accurate but some say otherwise. but basically i just need the shortest m4 that is the most accurate (so the scope could be reliabe) and can reach 480 fps. if needed, what modifications should it have?...