Highlight fireflies

Hello fellow Corona users,

I’m busy with a scene which has a strong dof and is lit by a sunny hdri. The problem is I can’t get rid of the fireflies that appear in the highlights. I tried various solutions but nothing seems to work properly:

Changed the sampling balance to different settings (from 16-2 to 4-2 to 8-4 and so on) as explained in the different topics about this problem.
Blurred the HDRI
Changed reflection and refraction to a slight blurred reflection/refraction
Denoiser (firefly only and high quality)
Highlight clamping

The attachment is a rendered region of about 300 passes.

I am curious what else could work in this specific case. Thanks in advance!

Would you be able to provide a sample scene maybe? at this point it might be easier if people can have a quick go at it themselves as often with these things, it’s a fine balance between settings and approach.

Thanks for your reply and your willing to look into it. I will prepare a scene later today.