Board Thread:Questions and Answers/@comment-180.191.61.2-20160312063637/@comment-25386610-20160316221345

Well, maxing it out would give you:

400% * 120% * 120% (2x Fatal Double Stick Icicle  or  Extraordinary Limited Edition Cookie Comics) * 112% (Bright Cookie)* 115% (Brown Balloon) = 741.888%

This is considering you play on a floor with Cookie and Pet power allowed.

If you want more XP per run, I would go with what Tricoro said and use Slower Energy Drain.

If you're just going for highest average XP per second, go with that combi. Note the level with pet and cookie power though.