It would probably be easier for you to tell us your upload speed, and we can tell you what quality it is reasonable to stream at with that upload.
It also depends on the game. If it's high-motion, like with FPSes and MMOs, you're going to need more bit rate for it to look good. For low-motion, like RTSes, you won't need as much bit rate for it to look good.
Asking for a minimum bit rate for a give quality setting is hard to define, since quality is subjective. Technically, you can stream at 1080p60 using 200kbps, but the result will look like poop.
If you have super low upload, I don't recommend using 60fps at all. In fact, I would lean the opposite direction, recommending 25fps so you can dedicate more bit rate to improving the quality of each frame.
But Krazy is right, you're just going to have to experiment with it and find something you're happy with.
