Will overpowering by 75wrms kill my sub?

He is right. It is better to overpower a sub by 50-100 watts than to have it underpowered. Most songs play the most by parts at around 10 percent less watts. For example, say you have a 1000 watt rms amp with a 1000 watt rms sub: The biest parts of most songs will then play only 900 watts, which is slightly underpowered for that 1000 rms sub. To make up for this, car audio experts counteract this by slightly "overpowering" the sub. By giving that same 1000 rms sub an amp that throws out 1100 rms, the biest parts of the songs will be 10 percent less, therefore, the biest parts of songs would play on that sub at 990 rms watts. Almost a perfect match for that sub!. So it is always good to get a slightly higher rms amp. Even crutchfield.com says this. They call it headroom. Hope this helps.