Probably a stupid question but...

[supaman]

You cant really answer this question since This depends on many things like
- GPU
- optimization of code
- RAM
- the game that you are running
As this emulator develops it will rely less on the CPU, the more the code is optimised the faster the emulator is gonna run, its just that when something has powerful hardware it doesn't need all these optimizations and runs well without it.
Hope I helped

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If you have a game in mind tell me what it is and what device you are using and I may be able to predict it for you