oh my... 2/3/4 u is to indicate the weight of the racket.. and the other one will be G3/4/5 which indicate the size of the grip i think u should find out more details in this forum...
http://www.badmintoncentral.com/forums/showthread.php?t=7726 Yes, there is a difference. Some people prefer overall lighter rackets, while others prefer a more heavy racket. Its up to preference tho.