if my speakers say 50 watts rms and 150 peak, is it bad to keep cranking them to 70 watts or even 100 watts with my amp which puts out 111wattsx4 rms?? is it bad for the speakers??

 

Well, if you push it long enough, your speakers will eventually blow.

Power Handling (RMS)
The maximum continuous sine wave power that can be dissipated by a speaker without failure, measured in watts RMS. Most speakers fail for one of two main reasons:
1. A speaker is driven with too much power, beyond its rating, and it overheats.
2. The amplifier is driven into clipping, producing square wave distortion that destroys the driver.

RMS Power vs. Peak Power
The amount of continuous power, measured in watts, that an amplifier produces is called RMS power. The higher the RMS figure, the louder and cleaner your music sounds. When choosing an amplifier, the RMS rating is the power rating you should pay most attention to.

Also, keep in mind that some manufacturers calculate the RMS power ratings of their amplifiers at different input voltages. For example, an amplifier rated at 100 watts RMS at 12 volts can produce considerably more power than an amp rated at 100 watts RMS at the more typical 14.4 volts.

Stereo manufacturers often display peak power ratings on the face of their products. The peak power rating tells you the maximum wattage an amplifier can deliver as a brief burst during a musical peak, like a dramatic drum accent. The RMS figure is more significant.

http://www.crutchfieldadvisor.com/IS..._glossary.html

 

say one has a sub which is 500watts rms and 1000 peak.
the amp that this person is using puts out 400rms to 600rms, depending on the voltage(12-14.4). Would this person run into ANY problems constantly setting the gain to the max or should he/she be concerned?

 

There is a proper way to set the gain. If it is set properly, no problems should be seen.

An easy way to set the gain...

-Turn off all Bass Boost or LOUD on the headunit. You want to keep everything flat and level.
-Make sure the gain is as low as it can go.
-Put in a familiar CD
-Turn off your interior speakers, itll be easier if you only hear the sub.
-Find out your MAX volume on your headunit. Lets say it is 50.
-Turn the volume to 90% max, so about 45.
-Slowly turn up the gain, as you get higher and higher you will reach a point where the sub is just distorting. Stop there, and bring it back down a notch.
-Now you have your gain set. Remember not to max out the volume on the deck.