It's working well for me so, considering it's pretty hard to roll back updates for QuickTime (it's heavily embedded in the system), I recommend trying to fix the current version instead.
Start by deleting the QuickTime preferences - com.apple.quicktime.plugin.preferences.plist and com.apple.quicktimeplayer.plist although it is only that last one which will probably have any chance of being effective.
Deleting these will reset the buffer size for streaming videos (among other things) so if you still are having trouble, go into the QuickTime Preferences (through the QuickTime menu in QuickTime) and in the Buffer tab, pull the little pointer across to the right. 🙂