Highest Ornn E damage possible

Ornn's E scales off of bonus armor and magic resistance. Assuming both hit, he deals 300 + 60% bonus armor/magic resistance physical damage. So how high can we go?

Those items together give 570 bonus (300 armor/270 mr). Scaling runes can add an additional 85.8 (47.5 armor/38.3 mr) bringing us to 655.8.

From masteries we can get an additional 100 (50 / 50) flat bonus under our tower after taking damage with 5 enemy champions present plus a additional 15% multiplier, bringing our total bonus to 755.8 + 15% bonus = 869.17.

60% of that is 521.5

That means we can hit everyone for 821.5 physical damage in a knock-up, not counting brittle, while having really, really huge resistances albeit very low life. Fun!