Discrete GPU throttles after rMBP (late 2016) has been on for a while
Our work lab Mac typically run very well for a week to a month between reboots. On high Sierra, since the initial build - we are seeing stability degrade from hours to days instead of weeks. 

If you can report your details - tests, scripts, sample files or apps - to Apple, you'll likely get some sort of explanation or learn when it’s fixed. In fairness, this isn’t unusual for beta and for new system chipsets and both of these are in play. Also, most of our apps are absolutely not ready yet and the filesystem is also still being tuned, tweaked and functions rolled out.