I prefer installing a generic fan that's one size bigger but lower RPM instead of a fancy Noctua. You end up with similar or higher CFM. Downside is it may require drilling extra holes. But it's much cheaper and I didn't measure but I bet it's quieter too.

I have done a few casemods for that exact reason, but also taken a few approaches other than a step-up in fan size. Based on the pictures of this case, for example, I would have drilled holes to add a second and third fan (of the same size) on the sides, and have all three run slower.