The FPS you stream at shouldn't affect the stream people watch tbh, if anything when people are getting buffering then it's usually a Twitch ingest server issue. Streaming at 60fps will more than likely cause the streamer to have performance issues but if it's buttery smooth then it's ok.
Couple of tips for new streamers regarding bitrates/FPS etc
30 FPS is more than acceptable for streaming. Higher will require a beefier PC.
60 FPS is good for local recording for uploading to YouTube later, but again 30 FPS is fine too.
Streaming is more about the Streamers UPLOAD speed & the viewers download speed.
If you stream at 10,000kb/s then your stream will look amazeballs, but not everyone will be able to watch it as they may only have 8mb/s download themselves. Plus the higher
bitrate, the more beefier the PC will need to be to transcode the stream.
2,500 - 3,000 kb/s is a good figure for most streams @ 30 FPS.
Slower paced games will look better in most cases as there's less camera movement/fast action.
First Person Shooters with lots of camera moverment/fast action will look blocky/pixelated at times. Consider dropping your stream to 720p for fast paced games to keep the image quality up.
I stream games such as Elite: Dangerous at 1080p @ 30 FPS - 3,000 kb/s bitrate
For something quicker BF: Hardline I use 720p @ 30 FPS - 3,000 kb/s bitrate.
Local recording I tend to use NVENC encoder via Shadow Play with very high settings to keep the image quality up, plus YouTube tends to destroy a lot of image quality when you upload it anyway, so don't expect crystal clarity on YT.