Dot3 is generally your cheap and cheerful, suits the same as most dot4 systems. Dot5 is a silicone based fluid but it ****s up most brake systems. Doesnt absorb water though I think. Dot5.1 is what you might call a performance fluid, good boiling point and decent resistance to hygroscopicy.
However, dot4 is the spec which has the benchmark performance fluids. The best fluids you can buy are dot4 (higher boiling point means "better" fluid) but these race fluids need changing every 6 months really because they love a touch of water.
The best fluid for everyday now is 5.1 or whatever is current, if you're considering performance then use a high temp dot4.
Cheers
) makes a good bit of difference, hasn't ever been changed in 14 year?? since new anyway, less travel on the peddle before it bites and when it dose its shorter (less travel) and is a lot firmer as well, so there must have been some contamination (not surprising after all them years) it took 2lt of DOT 5.1 to do it all, anyway they seemed to have done a fine job, and I couldn't have done it myself that cheaply with all the get and 2lt of fluid, OK I probably could have but for £50 all in, was it worth the hassle? I would have just saved a few ££ and if I had screwed the job up then it would have cost me a lot more
