There are two unpleasant things about this approach, which could simply be described as 'let's leave for Photoshop to fight with the noise instead of us'.
Firstly, the rendering time grows by the square of the linear size of the image. That is, a 1.5x increase in rendering size gives a 2.25x increase in time for the same number of iterations.
In the case of going from 1920x1080 to 2560x1440, this square is 1.77, which is also painful. That is, in a time of 2000 iterations on 1920x1080, you can only do 1130 iterations on 2560x1440.
Secondly, Photoshop knows nothing about the 3D scene, so conventional bicubic interpolation simply averages out the brightness of neighboring pixels and 'blurs' the scene. As a result, the renderer loses sharp lines even where they could and even should be preserved.
So if I usually do this kind of noise reduction, it's by using Depth Canvas (they can be rendered in Canvases, Advanced Render Settings) as filter masks. Because it's one thing to 'blur' the background, and quite another to 'blur' the main character in focus.
Another approach, not through Canvases, is to render the main character on a completely white background (backdrop 255-255-255) and without any light sources, then you get a black and white mask. But here you have to look at the intersections of the character with other surfaces, unlike the Depth canvas there are differences from the full scene (for example, the character may slightly 'sink' into the ground).
But such a mask is ready at once, unlike the Depth canvas.
If you prepare your work in Photoshop in this way, you can suppress noise there too.
Good tutorial, if your haven't seen it yet:
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