Again, speedtests are only an extremely small part of the problem. For diagnosing issues like this, they are usually next to useless. If you've verified your connection is behaving as it should, you've tried all different Twitch servers, and you are still dropping lots of frames, the only course of action left to take is to drop your bitrate until you stop dropping frames.
Unfortunately, there are just too many factors, most of which are usually out of your control, in regards to network conditions.