The mighty Cycles render engine has been getting a lot of performance improvements lately, with this latest one being improved sub-surface scattering performance.
Lukas Stockner has written a patch implementing Dwivedi guiding for path-traced subsurface scattering, which produces noticeably less noise at the same number of samples when compared to the classical path-traced SSS with no guiding.
In this first test, both renders are at 64 samples. The first render (no guiding) took 28 seconds, while the second one took 40 seconds. The new technique is slower at same sample rate, but offers much cleaner results, meaning a lower sample rate can be used for better results at similar render times, as seen in the second test below.
In this second test, both renders took 27 seconds, with the classic Path-Traced SSS at 80 Samples and the new Path-Traced SSS with guiding at 64 samples. The second image has noticeably less noise at a lower sample rate!