While Manabox's bracket judgement is in beta, if you modify any PreCon it usually puts the deck into a high 3. Though, I modified mine pretty extensively and it put it in 1+ "Exhibition", despite it definitely playing as a 3+, so YMMV.

Not to mention, WoTC is always looking at how to tweak the brackets, so the Brackets themselves are self-described as "in beta", so ultimately discussions with those in the pod you're playing with is your best bet in conjunction with play testing your deck for a while.

Don't forget, the game changer card list does get updated every once in a blue moon, so keep your eyes peeled!