Higher output volts does require you to turn the gain down. If your amp was set for 2volt preout the 4volt will be too strong of a signal thus giving you distortion. It will be a cleaner stronger signal which requires the amp to work less. As far as DB's go, at world finals I was running 2 JL500/1 with a phoenix gold PLD1 to each amp. One of the PLDs failed and I lost 5 DBs. I had to run the amp w/o a PLD and tried to adjust the amp best I could for my last run and still lost 1DB. So in my oppinion it does help BUT keep in mind.... PLDs was running at 8volts so going from 2v-4v might not be noticeable in DBs. My personal oppinion I would never run a deck with less than 4volts(w/o Line Driver). just me though.
