The kettlebell dead clean is an explosive lower body powered variation of the clean where the kettlebell starts from dead upon each rep. Out of all clean variations, the dead clean is the one that has the longest distance to travel.
What is the right speed to clean at? For power, you want to move as fast as you can and for any other goal the speed just needs to be such that the weight enters its ballistic flight.
What is the right weight to use for the dead clean? For power, you always want to work on increasing speed and strength, so you want to work with a heavy weight but not so heavy that you can't work on speed anymore.
For cardio, you want to work with a lighter weight than you would for strength and power, as you want to be able to keep moving for as long as possible. However, the weight should always be heavy enough to provide resistance for the explosive pull and ballistic flight. A weight too light provides no resistance and will flop all over the place.