When a single identity design must support very high external login volumes, performance becomes part of the architecture, not just feature selection. Salesforce Experience Cloud and identity features can support large-scale CIAM scenarios, but official guidance encourages validating expected login peaks and performance assumptions with Salesforce for unusually high throughput requirements. That is especially important when the solution spans communities and commerce experiences and expects more than a thousand logins per minute. The question is not just whether the platform supports federation, Person Accounts, or an external identity provider; it is whether the design has been reviewed for operational scale. Confirming performance considerations with Salesforce is therefore the prudent architectural step before finalizing the rollout model. This is why option B is the best answer in Salesforce terms.