I have a 36 BLM progressing to 50, a 41 WAR progressing to 50, my "main" MNK 50, and GSM at 50. Not too hard, I should think. FATE grinding seems a chore and is soul-sucking, while some dungeons (Brayflox's, Stone Vigil) are fairly lucrative for EXP grinding. I'd say ... stick with it instead of just doing ONE thing to level.