Redis cluster vs Redis Sentinel: when do you need a cluster?

we're currently running redis with sentinel for high availability, handling about 50k operations per second. we're projecting growth to 200k ops/sec in the next year or so, and are debating whether we need to migrate to redis cluster. my concern with cluster is the added complexity of key routing, hash slots, and dealing with multi-key operations across slots. is 200k ops/sec achievable on a single, well-provisioned redis instance with sentinel if we optimize our data structures and queries? or is that firmly in redis cluster territory? when did others decide to make the jump to cluster, and what were the biggest challenges you faced during and after the migration? trying to avoid premature optimization and complexity if sentinel can carry us further.