Each cape should have stats pertaining to the skill:
Strength: +10 strength
Prayer: +10 prayer
Attack: +10 slash, crush, stab attack
Defence: +10 slash, crush, stab defence
Magic: +10 magic attack and defence
Ranged: +10 ranged attack and defence
The rest of the capes could have like 1 or 2 in each bonus cause they dont apply to combat.