UNDOCUMENTED MECHANICS
"Chance to redeem soul" above follows a diminishing curve, not a flat gain per level; the other numbers in the same block do not: 23% at level 1, 55% at 5, 71% at 10, 85% at 20, 100% at the limit. Reaching the limit takes skill level 60, gear bonuses included, so the first few points are worth far more than the last ones.