You may not access widgets (or QPixmap from any thread but the "gui thread"), i.e. the drawing has to be done in the main thread.

You may, however, separate network communication, processing of the received packages in separate threads.

Another point is that more than about 20 or 25 repaints per second will keep the cpu busy, but will not help the user too much.
If you have more than 20 repaints per second, just update the internal data (w/o a repaint) and do periodic repaints (of this data) with a QTimer.
If you access this data from multiple threads, you have to protect it with a mutex.

HTH