The best streaming performance will come from default.htm or default2.htm in the Internet Explorer browser, because this uses an ActiveX plugin for all video playback and therefore it can handle more advanced compression than jpeg.
UI2 can only stream clips as a set of jpeg images for now. There are a few tricks to make it work better but nothing will make it perform as efficiently as the ActiveX plugin. Go to UI2 settings and under the "UI Behavior" category scroll down to the "Clip preview animation enabled" option and uncheck it. You can also use the Low Quality mode as I described in post #1365, to trade resolution and quality for speed.