60 -> 61 has always been pretty fast for me, unless you intend to use roulette exp on something else day 1 I don't see why it'd be slow.
Leveling -> Trials -> alliance -> Gubal -> Done. Has always gotten me to 61 on the couple jobs I've boosted, or like within 1-2 fates worth of exp to ding it, and only takes 1-2 hours.