Konteebos
Surfing on the lake of fire
The carbon-carbon material of disc and pad is poor at conducting heat, this means you can run the brakes much hotter, so improving cooling with the air flow, without heating the fluid.
I think the old standard AP600 brake fluid was pretty much as good as it got and boils (when fresh and dry...) at something over 300C.
I used to use Castrol SRF in my rally car, it boils at 325degC, but it is very hygroscopic and I had to change it after every event. Fed up with the expense and hassle I switched to regular dot5 and never had any problems - probably because I was competing mostly on tarmac and hardly ever used left-foot braking.