Lower latency is definitely a thing. With FPGA it's possible to 'chase the beam' like the original hardware, and have much reduced input latency from devices, etc. With an emulator you're going to be fighting the OS and the frameworks you built on top of. Even if you go "bare metal" (like my friend's BMC64 project which runs a C64 emulator like a unikernel on the RPi with no OS) you are still dealing with hardware built for usage patterns very different from the classic systems. You're always going to be one or more frames behind.