That is what would be my salvation. I am trying to do an overcast scene, with a finely displaced, slightly reflective ground, which in SR I would do by unchecking RT in the reflective shader. Only RT in the puddles, by decreasing the mask, very simple... and fast. But in PT, rendering comes to a virtual standstill over the displaced reflections on ground, whilst they needn't be very accurate and really reflective at all.
So, until I have a super computer, I have to either use no reflections, or use SR.
There's probably no way to overcome this, is there?