Ok I tried messing with the StackLevels, and it’s performance impact varied greatly per scene. One trend I noticed though was that changing StackLevels from 1 to 2 would harm the performance relatively drastically (on some occasions 5ms) but subsequent levels had less and less of an effect. In some indoor scenes I even raised the StackLevels to 6 without a noticeable performance impact. Also I would like to quickly mention that all of the data I took was taken in-editor at 1080p. I retested in a standalone window and some of those tests nearly doubled in performance. The exceptions were StoreEmittanceInHdrFormat, which ran stupidly slow no matter what I did, and MultiBounce, which took more processing power to run than it was worth (would love to see that optimized a bit, it typically doubled the GPU time!)