Some updates here. This horse picture above took me 1h to run 100 iterations on a 9 px blur.
I have found an algorithmic way to accelerate the convergence of the algorithm + I have done some more Cython optimizations. Now I run 705 iterations in 22 min with a 7px blur for the same result.
Plus I have changed my algorithm so that the blur is computed in a separate step from the picture, meaning that the PSF can be stored and saved for later with 75% of the job already done.
The work continues on the Darktable version, with new hope with these figures.