The lifetime of a bearing is to a high degree influenced by the temperature in the bearing's housing. Two factors control this: the temperature of the surroundings and the movement. For a design where the bearing is exposed to high temperatures, the PV value for the bearing should be low.
The temperature resistance is generally poorer for compound bearings than for metal bearings. I particular, thermoplastics have poor heat resistance. They also have a high thermal expansion coefficient. To achieve the necessary safety marginal, for these bearing materials, requires careful calculations during dimensioning.