This study assesses quantum-safe virtual private networks to backbones of financial institutions that experience harvest-now-decrypt-later risk. It integrates hybrid key exchange with X25519 and Kyber, as well as KEM-authenticated TLS. A testbed is used to simulate metro, regional, and long-haul paths (10, 50, and 100 ms round-trip, 1 percent loss), measuring time to first valid packet, goodput, fragmentation, and CPU utilization, as researchers vary the MTU, NAT-T, and offload. The threat model includes passive recording, active downgrade, man-in-the-middle attack interference, and insider misuse: experimental MOS-PK 47, 48. Greater post-quantum artifacts and HelloRetry/IKE cookies challenges increase control-plane cost, driving cold-start latency to hundreds of milliseconds on very long-haul links. Throughput on the data plane remains several percent apart from classical. Jumbo frames minimise the CPU load of software gateways, and ASIC offloading can be used to prevent capacity loss. The primary failure inducers are path-MTU black-holing as enlarged handshakes cross mixed-MPLS and Internet paths. Silent drops are eliminated with MSS closer to 1360 bytes, deterministic DF policy, active PMTUD, and IKE fragmentation stabilizes rekeys. The study provides a deployment playbook that jitters and batches rekeys, pins cipher suites, and monitors golden signals, and advances a blueprint that is auditable. The ability to migrate PKI with hybrid or cross-chained hierarchies, OCSP stapling, uniform telemetry, and cohort-based promotion provides the needed crypto agility without breaking service levels. The feasibility is proven, and regular validation and reassessment drills address residual risk.