hi @michaelmonte ,
I have looked at the Nvidia CUDA and LGPU kernel code. When originaly written, the code went and called CUDA code to ask how many GPU cores were on the GTX graphics card and then shared out the baking based on that number of cores on .
Therefore as newer RTX would many more cores on them the code went faster and hence your card, as does my old GTX graphics card, get much hotter as they work at full capacity. your RTX 4070 has 5888 CUDA cores
The fans start running at full speed to cope with the increased workload.
The reason Epic GPU Lightmass runs cooler is they use Directx DXR and cannot access the number of GPUs available.
Epic Epic GPU Lightmass therefore had to have a fixed number and this seems to correspond to the RTX 2060 with 1,920 CUDA cores. Directx DXR was made to support Nvidia and the new AMD graphics cards.
Therefore RTX 4070 using LGPU runs hotter because it using over 5000 cores to bake.
Epic GPU Lightmass uses about 1900 cores of RTX 4070 and therefore runs cooler as this is only 38% capacity of the RTX4070. Basically, to use a motoring analogy, RTX 4070 never gets out of first gear with Epic GPU Lightmass. When running with LGPU it runs like a Ferrari.
If you really want to try and see how fast/hot your GPU can go try this it even works on GTX1050 and getting 67 FPS!.