the PLA is strong enough for the larger gears, the bevel gears are very small and right on the edge of a .4mm nozzle being able to print them so nylon will take the higher temps in the smaller area and produce a better bevel gear. the nylon can also take shock loads with out cracking off the gear teeth. you will need to come up with your own formula for printing them on your machine. the small bevel gears should rotate on the shafts so you may need a set of MM drill bits so you can resize the holes for the shafts. i use all steel shafts in my trucks so i have changed the bevel gears from 1.75mm to 2mm shafts. all my large gears are printed in PLA. if the gears fit very loose or skip under load then you need to readjust your printer as the tolerance is too loose and the gears moving around too much. you can compensate by increasing the extrusion multiplier. carbon fill not printed correctly can be brittle. you will need to run tests to see if you are printing too cold or too fast. otherwise go with PLA it is strong when printed correctly. also carbon filament requires a hardened steel nozzle.