sunsky- samples 128, ibl- lock false, samples 200 are recomented from developer . Ya it smooth and reduce the reflection size but 2-3x time to render. [8-}]
Indsead of tweaking sunsky and IBL samples use samples in image property .
image {
resolution x y
aa 0 2
samples 46
filter blackman-harris
}
Ya its also affect rendering time but slightly 20%-30% less usage than sunsky and IBL.
[*-:)] But have a good advantage is add more samples like 60-80 and change anti-aliasing sample to box/triangle and its value min=0, max=1 to save rendering time.
[Tried only in one scene need some more time to confirm.]