I just realized something earlier today.
Kayle's E. Righteous Fury: "These attacks splash, dealing additional magic damage to her target and nearby units take a percent of her attack damage plus magic damage. This splash damage does not affect turrets." At rank 5, the AD ratio is 40%
Runaan's Hurricane: Unique (Ranged only): Your basic attacks fire minor bolts at 2 nearby targets, each dealing 10 + 50% of your attack damage and applying on-hit effects.
Combined, this means when Kayle AutoAttacks:
-Kayle does 100% AD from her AA to her original target
-Kayle's E does 40% of AD to nearby enemies
-Runaan's Hurricane does 10+50% of AD to nearby enemies
____E + Hurricane = 90% AD per AA
Assuming Kayle is targeting 1 enemy between two others (total of three close enemies), the Total Amount of AD per AA is 280%.
And assuming Kayle is building lifesteal, Hurricane essentially doubles lifesteal. If she has 10 lifesteal, this becomes 20 lifesteal if there are 3 targets. 20 LS= 40 LS. 30 LS = 60 LS. Combine Hurricane with BoRK = everything dies while you heal up with ease.
I need to try this out in-game, I'm going to have to Jungle Kayle tomorrow.