The DOT classifacation is just a minimum spec that the fuid has to reach.
DOT 3,4 and 5.1 are suitable for road cars. DOT 5 is NOT hydroscopic, ie it doesnt absorbe water. The
problem with that is that any water you get in the fluid will just collect behind the piston and when the brakes go >100 deg C you know what happens. The others absorbe the water throughout the total volume of fluid.
The one good thing about DOT 5 is that its totally non corrosive and not very flamable. So if you fancy changing your fluid every wekk then you can prob use DOT 5.
Me i use ATE super Blue in my Porsche, it does NOT make brakes squeel only Pagid pads do that. But Pagid Bluse are the business.
Castrol SRF fulid is slightly higher dry and more importantly wet BP than ATE super blue but its costs 5 times as much!!!
Super blue all that way, good value and high Dry and Wet BP, much much higher than any DOT 5.1 fulid out there.