With preamp voltages, higher is better for signal-to-noise. Think of it this way..
If you were sending 2 volts (old standard) to your amp (or sub) and you're getting a random noise (let's say from the fuel pump) thats about .5 volts (which is a lot, but I digress..), your amp of course is going to boost both up equally aka about 1/5 the signal will be noise (.5/(2.0+.5)), whereas if your preamp is 4 volts it would be 1/9th of the total signal(.5/(4.0+.5)) ...
Now, if you've wired it up so that the system won't catch any noise, then none of this matters.. and and you might want to start competeing, hee.