Marginal benefit measures the consumer’s benefit of consuming an additional unit of a good or service, while marginal revenue measures the additional revenue a company earns by selling one additional unit of its good or service.
Productive efficiency has nothing to do with either MC or MB
Allocative efficiency is when MC=MB but that is for the consumer; it is not the same MC as for the producer.
When the price (cost to the consumer) is lower than MB to the consumer, there is consumer surplus:
Profit maximization for the producer is when MC = MR (this is oversimplified theory here, not reality) for the producer, not the consumer.
For example, MR is not always the price per se. It is the price in perfect competition, where the firm is a price taker, but is not when the firm can affect prices (such as a monopoly)