UNDOCUMENTED MECHANICS
"Physical Damage Received Reduced by", "Ranged attacks slowed to" above follow a diminishing curve, not a flat gain per level; the other numbers in the same block do not: "Physical Damage Received Reduced by": 6% at level 1, 20% at 5, 27% at 10, 33% at 20, 40% at the limit; "Ranged attacks slowed to": 68% at level 1, 50% at 5, 41% at 10, 33% at 20, 25% 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.