will you notice any deferents between a deck with a 95 db signal to noise ratio or a deck with a 105 db. With 2 volt out puts and also the same ? with 4 v out

No.

No way, no how to either question.

Think about how loud your car is. As long as your noise floor is below that you have nothing to worry about. Having a dynamic range of 100dB is way overkill in mobile applications.

As for the 2v vs 4v the only difference will be that you will have your amplifier gain turned a teeny bit higher to compensate. If you have a deck that you can hear the acoustic difference in each step of the volume knob then on a 4v deck you will be only outputting two volts one step down from max volume (max no clip level). If you can't hear the difference it could be a couple steps or if your ears are stellar. Again either way it is easily compensated with the gain knob on your amplifier (and in fact why your amplifier has a gain knob).