Well just so u know seal, when i hit 50 i grinded the first level in just the lvl 50 abyss with a decent full party. We was killing about 40 mobs every 3 minutes with 350ish exp a kill. Try that for your first level as there are no repeatable quests. For level 51 i did the repeatable quest along with abyss to hit lvl 52, if this became boring i completed some quests i had but did not hand in for the rewards.
If need be i suggest you save quests for 57+ as you basically have 1 repeatable quest till 60, the quests really dry up during this period so you will need them
Jun