I have no E cores myself but I have read it is best not to use them. Not sure how to make that happen.
I am using x99 and x299 boards and an older 2P xeon rig.
As far as fitting tasks in L3 on PG task preference it tells you how big the tasks are. (FFT size)
Recent average CPU time: 113:33:14
FFT sizes: 2560K to 3072K (uses up to 24576K cache per task). So that would be around 25mb
Most intel CPUs it will fit or it won't. AMD CPUs can be a bit tricky they way the cores interact with the cache.
If you do ever want to run PG in the future, as of now CPUs with AVX512 run the fastest, Intel X299 or the new AMD CPUs
WCG still has medical tasks too and I have been getting steady tasks.