A question I cannot find an answer to. Full burst runes?

Let me start off by saying I know going glass cannon runes is not ideal, not here to debate that. So I have been playing morde a lot lately. And have noticed it is VERY easy to out sustain most people with my current ap/armor/mr runes. But I want to try full ap burst runes.

With all teir 3 runes for AP, magic pen what in your opinion is the highest damage setup for early burst (not interested in scaling). I have tried 15ap/15magic pen and many other combos. More ap? More penetration? What is more damaging for early game?