Dauntless;c-160594 wroteI've never seen DOT 5.1 in shops. I always use Nulon Xtreme Performance Super DOT 4, and I've towed cars down mountains without issue.
Apparently SuperCrap stocks DOT 5.1, but once I read what it was for (offroaders that wade, basically) and it's downsides (squidgy pedal feel & potential basic incompatibility with systems designed for DOT 4) I just ignored it.
Yeah Nulon is another brand which I know is good for general oils, so was one I was considering for a better performing brake fluid. I think the Nulon Xtreme is also more widely available, so if that's worked well for you I might just grab a litre of that.