Pantheon: AD vs ArPen runes

I've always wondered where could I apply ArPen runes and good ol' came to mind since he's said to be in such a sinergy with that stat. Thus I'll compare a 15 AD (marks + quints) asset vs a 10 Arpen + 8 AD (8 ArPen marks + 1 AD mark and 3 Quints) one. I'll consider Martial Mastery (+4 AD), Brute Force (+10 AD at 18), Warlord (+5% bonus AD), Devastating Strikes (+6% ArPen and MPen). I'll make up two scenarios, one for lv. 3 ganks and one for lv. 9 (midgame) skirmishes. I only use him as a Jungler so, I'll analyze for his build in that role.

LV. 3, Q,W,E at rank 1, only item, 60 base AD, opponent has 40 armor.

The full combo I'll assume is: Q->W->AA->E->Q (not critting), which deals [W magic damage is not taken into account] 65 + 1.4 bAD + 60 + 1.0 bAD (AA)+ 80 + 3.6 bAD + 65 + 1.4 bAD = 270 + 7.4 bAD

AD RUNES bAD = 23 ~; ArPen = 6%; Combo deals: 440 dmg; Mitigated damage = 320 dmg

ArPen RUNES bAD = 15 ~; ArPen = 10 + 6%; Combo deals: 380 dmg; Mitigated damage = 298 dmg

AD deals 7% more damage = 22 real dmg

LV.9, Q rank 5, W rank 1, E rank 2, , 75 base AD, opponent has 70 armor.

The full combo will deal 665 + 7.4 bAD

AD RUNES bAD = 121 ~; ArPen = 20 + 6%; Combo deals: 1.560 dmg; Mitigated damage = 1070 dmg

ArPen RUNES bAD = 112 ~; ArPen = 30 + 6%; Combo deals: 1.494 dmg; Mitigated damage = 1100 dmg

ArPen deals 3% more damage = 30 real dmg

TL;DR: It seems AD runes work slightly better in the early stages of the game while ArPen begin to get better (by minimum proportions) in the mid-game. When the game goes further on, 10 ArPen becomes quite meaningless against tanks and slightly armored squishies ( ), where & play the main role (BC full stacks + LW + Devastating Strike grant 55% Armor Penetration !!!).

Aaaand, yea, I probably stated the obvious. Just wanted to put these calculations on "paper" and share with someone who might be interested. Hope I didn't make mistakez.