The 600MHz neighborhood is also where USB runs out of steam on a bandwidth/framerate scale if you're not running ASICBoost. If you're not connected to an AB-enabled pool, it won't matter if you have it running off a Cray, you won't get much more than about 800GH.
GS miners all have an Arctic Silver ceramic white thermal paste applied, so whatever they recommend for lifetime.
PI4 using the USB3 getting 800mhz 1th on both on one PI4.