If you quit your job, would it be easy to pick it up again? If you are not earning, you may find yourself in a situation needing more money to get that extra vital rating. Similarly, your job whilst providing an income at least during the ground theory D/L stage may be holding (or stressing) you back both mentally and physically in which case studying may be difficult.
http://www.pprune.org/forums/showthread.php?t=131649 is a golden thread to churn through.