Clifford matrix is the same as Viper. Clifford's concept and intelligard series are still a league of their own even though they are owned and made by the same people (DEI) No matter what the install makes a much larger difference than the alarm that you use. I prefer Clifford, but honestly have no complaints about Viper (besides the fact that the sensors aren't remotely adjustable.) To answer the origional question, the 791 is the newer model of the 790, there really isn't much of a difference for the consumer besides the carbon look remote on the 791 where it is a tanish grey on the 790.