Some tests - 1.6 hf1 vs 1.6 hf2:
1. DOF
Speed and noise quality is similar, but in hf2 you don't get the "patterns" in strong dof, manifested by the "holes" in blurry areas.
2. Interior with UHD Cache - 5 minutes
Generally lower noise level, and the noise patter is more "pleasant". Also more details are visible in the noisy areas - e.g. on fine textures, when there are subtle shadows, etc.
3. Rounded corners
One pass: