I run DOT 5 in my disc/drum system and it works great so far (years). I did find the hard way that it gets past the seals in my Howe clutch slave (pull) cylinder... rebuilt the slave, flushed the master and line, and now that master has DOT 4.
The urban legend that bad things will happen if you mix silicone and glycol fluids is still around, I see. NOTHING happens. No atomic fusion, no explosion, no "goop" formation. I have done it myself in a glass jar. They don't mix (the silicone floats on top the glycol) but there is absolutely no reaction. If you wait long enough, the purple dye in the silicone will migrate into the glycol. That's all. The fluids still don't mix. Can you imagine Dow Corning's liability if everyone's brake system blew up from accidentally or purposefully adding silicone fluid to one that had, or used to have, glycol?