I'm sure that Shimano has done their homework with regards to the hydraulic fluid but I wonder if something from the automotive world would make the system even more robust. Back when I was going to track days, I used Motul Dot5.1 fluid and that solved my issues with brake fluid boiling. It might be overkill for bikes but anything to avoid that oh sh*t moment when you grab the brakes and the lever goes to the bottom.