Please stop trying to stack haste over mastery. Haste will never overcome Mastery in a way that almost all encounters are multi-target encounters. On multi-target encounters you want to put bombs on everything, and use arcane explosion/glyphed coc most of the time. For those situations, Mastery completely destroys haste.
In what situation does haste really perform better than mastery? I think none. Everyone is troll nowadays, everyone has meta gem. Going haste over mastery would mean you would be GCD capped on Arcane Blast in many situations, and would also suffer from lower bomb/aoe damage.
