On my 3v, when my rims element died, i tried the hermit with a single kettle element to do the full job. Best i could get is 1/3 degree per min. Thats a 100l mash tun pushing a 112l batch (final vol) and the march 809 on full flow.
Biggest element in use i know of is 3,000w.
My mate in brissy...