on this one i think i got a bit lucky - there was just a minor bit of crustiness in a couple of places when fully zoomed. one trick i do know is to decrease the Raystep multiplier and Stepwidth limiter on the Calculation tab. looks like they default to 0.25 and 0.3 in high mode, respectively. i'll drop them down to 0.05 and 0.1 respectively if i'm seeing a lot of spotting. increases your render time by quite a bit, but it makes a big difference. hope that helps.