We recently benchmarked Vault Enterprise (self-managed) across the KV, SSH, and PKI secrets engines on a HashiCorp Validated Design AWS deployment, ramping KV load up to 500 virtual users with k6.
Memory, not CPU, turned out to be the real ceiling. CPU stayed in the 20 to 40 percent range even under heavy load, while memory hit 100 percent utilization at 500 concurrent users.
For SSH certificate signing, ED25519 pushed the concurrency knee point to roughly 200 VUs, about double what RSA-2048 handled, at a fraction of the CPU cost, roughly 40 percent versus 92 to 96 percent for RSA at comparable concurrency.
Full write-up covers KV payload size effects, PKI latency behavior, and storage and tuning recommendations: https://www.hashicorp.com/en/blog/understanding-vault-performance-benchmarks-from-real-world-workloads