I took my Astrologian from 30 to 50 in 2 days by FATE grinding, dungeons, and doing the Large Leves in Ishgard when I reached 45. I burned all 100 of my allowances and got me straight to 50 so there are dozens of options. You just gotta find one a little less boring than the last in order to power through it. Hitting level 48 gave me the drive to stay up the extra 3 hours last night to just get it done to 50 :3