I have generated the following gif from a clip captured from a NES emulator.

I generated with the option --fps 60 on the command line, but the resulting gif is too slow. (tested in different browsers)

Here a properties from the Media Player:
Video: LAGS 256x224 60.1fps 14667kbps [V: lagarith, rgb24, 256x224, 14667 kb/s]
Audio: PCM 44100Hz mono 705kbps [A: pcm_s16le, 44100 Hz, 1 channels, s16, 705 kb/s]

I used the docker version for the conversion:https://github.com/maxogden/gifify-docker