My shaman aren't 45 yet, but when I PLed my druid, I took him to 45 in SM cath, still getting decent XP.

Keep in mind the XP you gain per kill actually goes up as you level, because you are receiving less of a penalty for having a 70 in with you. If you don't have a 70 GG, I bet you get a ton per kill. If you don't want to do ulda, just do SM till 45 then try ZF again.