YouTube isn't the fastest here in Germany either. For example the Telekom (Germany's largest ISP) has bandwidth troubles with YouTube from time to time (because of some backbone bottleneck). I could only find a German blog post about this, but I have definitely experienced this myself: http://stadt-bremerhaven.de/telekom-aeussert-sich-zu-youtube...
Here's my bookmarklet (doesn't work on embedded videos in iframes, I assume because of same-origin-policy)
javascript:void%20function(){document.querySelector(%22video%22).playbackRate=parseFloat(prompt(%22Set%20the%20playback%20rate%22))}();