A 16 MHz 68000 or 80386 can emulate a 1 Mhz 6502 or 4 MHz Z80 machine at full speed, no problems.
A 3+ GHz modern machine doesn't even notice such a task.
True. But some emulators are simple/inefficiently written and/or (puns accidental) logic simulator types, coping with ancient discrete logic cpus (e.g. TTL). This can result in poor performance of the emulator, hence the want/need of a faster cpu, usually single thread performance wise.
30% faster would be 46 FPS vs 60 FPS, not 41.
But in any case game FPS seldom varies much at all with different CPUs, it's all in the GPU.
You're right, I did a poor job, with the frame rate estimation.
Too off-topic and OP not interested, so I'll keep it short. As well as the GPU (which is usually the primary factor dictating FPS), the cpu can affect frame rate, especially with some games. So, if too low a FPS is making the gaming experience bad for a particular player. As well as getting a very powerful gaming card, they may also need to get a very fast (especially single thread performance, but enough cores (6+ I guess) with some games as well), cpu. Otherwise, the frame rate can dip, and the picture breaks up (distorts/lags/looks like a slide show), in a way, which annoys some gamers.