Ok, I did some strong test. I did these two test. Unfortunately, I had to change slightly the shader. But for this purpose isn't so important.
Resolution: A3 300 DPI = 5000 x 3500 px
Progressive = 24h
Bucket= 22h
I don't remember exactly the Progressive parameter. I think: PTS: 8 or 4 and LSM 2 or 4 .
Bucket: Int samples 32 - Pass: 10 (5 reached in 22 hours) - Adaptive threshold: 0.05
As you can see, with bucket I have a little bit more noise in the wall and in the uniform area, but the DOF is much better, in less time.
I hope Ondra find the way to solve this problem (DOF) in progressive mode.