I researched my problem a bit more and found out the following:
Dot 5.1 brake fluid will resist slightly higher temperatures than Dot 4.0, however it absorbs more moisture and must be changed frequently. High temperature Dot 4.0 is almost as good, and costs much less, and doesn't require changing near as often.
The solid disc rear rotor offers a larger area to absorb heat and works better in muddy conditions. Without holes drilled in the disc there is less dirt and mud getting between the pads and disc.
I changed my brake fluid, refilling with Motul 600 Dot 4 and switched to a solid rear disc. Went riding yesterday, descending 4000' multiple times with the brakes preforming perfectly.