Length for length’s sake is not good.
If a tale can be told well in 45k words, it should be told in 45k words.
Bulking up a sex scene to absurd duration just to meet your publisher’s 50k wish is not worth it. Trust me on this. Even the most voracious of your readers will tire of manhood grappling, bosom nuzzling, derriere pinching/spanking/biting/etc. if they are all piled on top of each other in a single horny romp.
If you must find that extra 5k somewhere, add an entirely new scene.
Remember: when it comes to sex scenes, no matter what they say, bigger is not always better.
Until Monday (another travel day tomorrow, I’m afraid)…
Post-note: I still struggle with this. In fact, I’ve been known to cover up the handy-dandy word counter with a post-it note while writing. Only once I’m thoroughly happy with the scene will I peek.