I've come to the conclusion that there is some kind of restriction being placed on international bandwidth. It's not a hard number but a percentage of your line speed, a very low percentage. For me I have a 10mb sync line that only does ~200 kB/s to twitch.
It doesn't affect youtube so much because of local caching. Which is why if you watch an unpopular/obscure video on youtube the first time you try stream it you get very very very bad quality, because you're trying to get it internationally. If you click refresh magically you'll get your line speed on the same video because now you're getting it from the locally cached server. Twitch however has no local cache server and so you'll never get good quality out of it unless you use a third party app (thanks i got issues

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I'm not sure if AH know about it and are doing nothing or if their international provider is doing it without them knowing but I'm going to keep bringing this issue up until they fix it. I like using twitch and I'm sick of watching in low quality when I know my line can do 1080p.