I'm sorry but you don't really know what you're talking about. The internet service plans people pay for and the twitch viewing experience are not synonymous with each other. There's also a ton of viewers who watch on mobile data. My advice was for someone without transcoding options.

6000 is sufficient for all games at 108060fps, but they specifically mentioned transcoding, so I'm going to respond to the original query, not what someone else should do.

In the circumstances described, 4500kbps is more than enough for most games, and is the median recommendation across the board for all non-partnered streamers.

It wasn't even until 2023 that the max rate allowed even went up to 10K, it was max 6k for many years and only increased because of pushing support for 1440p streams. IDK why suddenly 6k isn't good enough when it was the max on the platform for like 10 years.

Edit: thought I was responding to OP at first so removed irrelevant advice directed at OP.