Formula to train healing with cure is (Poison level*20+15)
So level 1 is 35 diff ( snakes, plagued rat and bats )
Level 2 is 55 diff ( Dark strangler, giant spider, green vortex minion)
Level 3 is 75 diff ( giant scorpion, phase spider, rock spider, frost spider, flaming spider, terathan avenger, ophidian avenger, giant serpent)
Level 4 is 95 diff ( wyvern, dire weaver, giant rock scorpion )
Level 5 is 115 diff ( poison drake)
level 6 is 135 diff ( glutton minion, poison elemental, poison dragon )
Gaining with cure can be abit slow, best method is probably to be like 15 points lower then the diff and equip items to get close to the diff then take off as you gain to stay at same level.
You can also gain by resurrecting people and that is 105 diff but you can do it with 90 in healing and anatomy.
Also just testing using your skills will show you difficulty messages to help you out, that number is way better then any infovault or anything like that.