Customer is evaluating Platform Events solution and would like help in comparing/contrasting it with Outbound...

 Both Platform Events and Outbound Message offer declarative means for asynchronous near-real time needs. They aren’t best suited for real-time integrations (A). In both Platform Events and Outbound Messages, the event messages are retried by and delivered in sequence, and only once. Salesforce ensures there is no duplicate message delivery (B). Message sequence is possible in Outbound Message but not guaranteed with PlatformEvents. Both offer very high reliability. Fault handling and recovery are fully handled by Salesforce ©. Number of concurrent subscribers to Platform Events is capped at 2,000. An Outbound Message configuration can pass only 100 notifications in a single message to a SOAP end point (D). Both Platform Events and Outbound Message are highly scalable. However, unlike Outbound Message, only Platform Events have Event Delivery and Event Publishing limits to be considered (E). Reference: Salesforce Integration Architecture Designer Resource Guide, page 23