hi @michaelmonte,
HDRI is not supported in CPU Lightmass and therefore LGPU ONLY Direct Light.
LGPU is a Brute Force calculation as its base code is based on UE4, where none of HDRI exists.
Epic GPU Lightmass works on Direct X Raytrace is a bunch of shaders which have support for HDRI.
LGPU will always be faster bakes because it works by allocate to each CUDA processor.
The blistering speed of RTX 40XX family is partly due to its over 8000 processors. This is still be supported in UE 4.26/27
For ArchViz community its very important as they still use 4.26/27