The advertised speed is not the whole design
A router connects networks; your edge device may also perform firewalling, NAT, VPN encryption and traffic shaping. Evaluate performance with the features you will enable. A headline forwarding rate does not predict encrypted throughput or behavior under congestion.
Locate the constrained direction
Measure upload and download during normal busy periods. Upload saturation can harm an outbound audio stream while downloading still looks fast. Inspect queue delay and drops at the edge and compare them with a quiet-period call.
Understand session state
SIP signaling and RTP media may have different destinations and lifetimes. Document provider requirements, address translation and firewall state. A WAN change can invalidate active mappings even if the new link is reachable. Test new calls and established calls as different failover outcomes.
Keep changes reversible
Save the working configuration and change one relevant behavior at a time. If a SIP-aware feature appears to rewrite traffic incorrectly, compare traces on both sides before deciding whether to alter it. Do not solve uncertainty by exposing the PBX broadly. Maintain a recovery path for remote administration and document how staff call when the edge device is unavailable.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.