If the plan is to move towards Ballistas and Sun Titan and lean more on white, might it be reasonable to move towards Eladamri's Call instead of GSZ? It's an extra mana the-turn-of and reduces the surprise factor, but gets every creature in the deck which would allow for more bullets and little synergies like Mephidross (not him specifically necessarily but just as an example). GSZ is a sacred cow in the deck, but desperate times and whatnot...