The built in emulator in PPC ROMs is for a 68LC040. Connectix Speed Doubler offered a faster emulator as part of its feature set. When the PowerPC Macs were released, they included was amounted to a fully emulated operating system since 7.1.2 was a quick modification to run on the machines. MacOS 8.5 should run faster on a 6100 since its mostly native PPC code, but that was offset by its higher memory requirements.