To be able to work high rates on contests there are several techniques. Popular is of course SO2R but there several methods to accomplish this. Jose CT1BOH suggested the 2BSIQ technique which is quite attractive.
The fundamentals are:
1. Send TX on radio A and listen with both ears on radio B.
2. When you end TX on radio A you get stereo mode and hear both radios in the ears.
3. When you start TX on radio B back to both ears to radio A.
All this done automatically w/o tilde button.
Here is a video demonstrating it. There is no CW side tone sound as you always listen to other radio for callers while sending CW on the other radio.
More about this technique from Joses material: http://www.qsl.net/ct1boh/2bsiq/?tube=.