Regulatory reporting → Cloud (batch, periodic, read-heavy, marginal savings real) ✅ - Dev/test environments → Cloud (obvious win) ✅ - Core OLTP (ATM, wire, posting) → Mainframe (Sysplex, 5,800 TPS, sub-ms latency) ✅ - Analytics warehouse → Cloud (CDC-fed replica, no write-back) ✅ - Mobile API gatewa