The 536M target
Rebirth 5 requires a Tier 30 nuke, which has an exponential value of exactly 2^29 = 536,870,912. Manual grind takes 8-12 hours; Auto Merge compresses this to 3-5.
Cash vs nuke value
Cash payouts from city raids (6-7 Quantillion per strike) are 10x larger than passive accumulation. Convert apex nukes into cash before Rebirth.
Post-Rebirth scaling
Rebirth multipliers stack multiplicatively with premium multipliers. Rebirth 5 + x2 Spawn Speed is the late-game sweet spot.