First of all...overpowering woofers (having more power than the RMS rating) is a good thing to keep motor temperatures lower. Having an amplifier with less power can heat the motors and cause failure due to the amplifier running out of power, clipping, introducing amplifier created square waves and eventually ruining the motor. When a loudspeaker is presented with amplifier induced square waves (amp distortion from being driven into clipping) the motor will heat up and the voice coil may buckle and lock.Suppose the eminance woofers are rated for 250 watts each RMS and you power the pair with 700 watts. You will be less likly to cause damage with this power if it stays undistorted. A 100 watt amp will surly clip and cause failure given time.
Best to go with as large an amplifier (within reason) as you can afford in a car stereo situation.
If you do not understand any of this...do a search on amplifier clipping and you surly will find some more explanations.
I suppose you will be using the car stereo at high volume levels. If not, you can get accurate bass from a good set of 8" woofers in the proper box and not need the higher power. If SPL is what you are seeking, you cannot have "too much" power. Now if your amplifier is more than twice the RMS rating of the woofers, the other extreme can burn out the voice coils from sheer voltage.
I hope this helps you.