Be sure you are not confusing DOT 5 with DOT 5.1 which are two totally different base fluids.
DOT 5 is silicone based, and DOT 5.1 is Poly Glycol Ether based, much like DOT 3 and DOT 4 are. DOT 3/4/5.1 are all compatible with each other and can be recognized by their clear color, even though the color will turn a dark rust color over time. The disadvantage to this fluid is that it is hydroscopic and over time, will absorb water which in turn lowers it's boiling point.
DOT 5 being a Silicone based fluid is not compatible with Poly Glycol Ether. DOT 5 can be recognized usually as a purple color. If added to a system that previously used Poly Glycol Ether, the reaction between the two fluids will cause any rubber parts to break down and leak.
If you taste them on the tip of your tongue, DOT 3/4/5.1 will be 'bitter', almost like anti-freeze is. DOT 5 silicone will taste 'bland', and almost like nothing... much like mineral
oil.
The primary advantage to Silicone is that it is non-hydroscopic. It will not absorb water as poly glycol ether will, therefore making is a much longer lasting fluid. The most significant disadvantage to silicone fluid, is that it is much more compressible than Poly Glycol Ether. Used in either brakes or the clutch system, it would give the clutch a spongy feel, and not present a desirable condition for a performance car of any type.
As an aside, The dry boiling point of DOT 5 Silicone fluid is 500º F and Wet is 356º F. However, Wilwood's economical DOT 4 based fluid has a 571º F boiling point, and the more expensive Motul is at 600º F.