To fill that gap on Assassin lvling...
lv 45- Jobchange: Leaf Cats, if you have a Priest you might want to try Parasites. If Leafs hit you too hard go to wolves, you kill them pretty fast and they are quite dense on the map.
Jobchange - 65: Get Grimtooth ASAP!! Then try to get 2 fortune swords and a set of Ele Katars (fire and ice are pretty cheap). You can do Minorous mobs w/o fortunes, or try yourself at Hill Winds where I would strogly recommend the fortunes.
After that, usual places would be High Orcs, Rachel 1 (or deeper if you have a loyal Smokie pet) or Anolians (which you can do up to 99).