i would run 8 gauge for the ground/power (the battery is right there, so it's not that expensive!) knowing davebret, i suspect he has 4 or even 0
are you sure the mbquarts are direct drops? looking at the mounting depth they would need spacers to lift them out of the door. i think mb quarts come with an adaptor for offset mounting holes? which is the other problem you have to overcome with door speakers.
i don't expect you to get much difference by swapping amps (unless the amp is just bad). you're limiting factor is the quality of the signal coming from the headunit and also that you're taking highlevel output from the headunit, converting it somehow to low level for the amp then converting it back to high level for the speakers.
