are the benefits of sex as great as with masturbation?

It really depends on the person. Some people have great sexual stimulation while masturbating but aren't able to get quite the same sensation during sex. Others have absolutely great sex due to matters of anatomy, emotional connection with their sexual partner, etc.

Many people, especially married people, consider sex much more stimulating and gratifying than masturbation because they have a wonderful emotional and sexual connection to a person with whom they're in love.