Hello, Im playing on official PvE 6010. I have spawned around 10 max surges (>=1000), most South and a few North and North east surges. It seems, but Im not 100% sure, all named/T4 thralls I have seen is from the Votaries of Skelos faction. I now checked the wiki thrall tables and at least all named I have kept happens to be votaries.
I use the west most Leyshrine.