I've been using G10, Micarta and carbon fiber from Current Composite lately; they also supply AKS, Pops and Masecraft with a lot of their material. No issues working it. 95% of their stuff is US made, which is nice!
Slowing down the belt speed is critical and I often dunk a sponge in water and wet my belts with it when sanding. Let the belt do the work; don't apply too much pressure. Pressure means more heat and can burn the material, especially paper micarta. I have a set of scalloped belts, 2" wide, 120, 220, 320, 400 and 600 and I get well over 25 handles out of that set of belts. I change belts out around once a year for handles unless I break one or rip it accidentally. I use 36-40 AO or Zicronium belts for roughing and initial contouring, then a scalloped 80 Klingspor belt to clean up the deep scratches and and get it contoured and the edges rounded, then switch to the J Flex scalloped belts.