This bug is related to QTBUG-15065:
I have problem with QSslSocket too. I've successfully implemented bandwidth limiting for QTcpSocket utilizing Torrent example code and it's author advices. Setting setReadBufferSize() for QTcpSocket throttles bandwidth down. However this approach does not work for QSslSocket: it read all the data available any way.
2nd bug in QSslSocket: I can't set buffer size higher than 32 768 bytes - it does not work either in this case - no transmission at all. Can send sample code if necessary.
3rd: if QSslSocket::setReadBufferSize() set to 0 - socket disconnects right after data download starts.