There is a tendency among a lot of writers to rely on profanity when they're writing a sex scene. To the writer who does this, all sex scenes have to have profanity. Someone has to be screaming “fuck me” or something for the sex scene to be readable (according to the people who rely on it).
Before you start writing your scene, here are some questions you should ask yourself:
1.) Who are the characters in your scene? Is it in their personality or their diction to use that type of profanity, even in extreme situations? If not, then your characters won't actually be in the scene you write. Instead, it’ll be charicatures of your characters.
2.) What was the build up to the scene you are writing? Was it two characters confessing their feelings in an intimate fashion, or was it just animal lust? The former sets into the story better with as little profanity as possible (preferably none). If it, for example, was an encounter in the backroom of a sex club, then feel free to go as heavy with profanity as you’d like because it sets into your story.
These are just my opinions. Take them for whatever little they're worth.