That's the best plan really, just ask someone to take you into hall of tournaments a few times and call a different wraith(s) each time and try and get an idea that way.
the min - max amount of damage they might do is pretty inacurate because it's one thing for a golem to fight a lvl 5 - 6 - 7 and a completly different thing to fight a lvl 9 - 10 ...
from lvl 9 up pretty much all summons become food for oponent meaning, he will rather heal on them not take damage from them
Evolution cannot avoid bringing intelligent life ultimately to an awareness of one thing above all else and that one thing is futility.