psi
#5
actually, if you wanted to get technical, you should run whatever pressures are listed on the sticker that's on your drivers door and not what it says on the tire. the tire is ALWAYS a maximum pressure and not a running pressure. hope that helps.
#6
About 2-3 PSI less then what the tires says is what I have heard. Less pressure=better handling but worse mpg. More pressure=worse handling but better mpg. Just adjust how you see fit, but don't take a turn too quick with Full tire pressure because you will not grip as well as before