Usually people go with a little more power. As long as you, or your installer, set the gains on your amp accordingly to your sub. You should have no problem running more power. Usually its about 25% more power than your subwoofers rms power rating (ie. 100 watt rms sub @4ohm..with 125 watts rms @4 ohm from amp).
If you under power your subwoofer by a little...it might be ok. But too much isn't good either. If your sub asks for 150 watts rms try to equal it or be over by a bit. For the times you really crank up the volume to near max, is when your amp is going to be working extremely hard to get that full power to your sub. So if it can't give the sub all the power its asking for, it can start to clip or distort. Or better yet you will over work it in the future and it may quit or overheat.
My 10'' is a 350-500 watt rms @ 2ohms. Right now the amp puts out 700 watts rms x 1 @ 2ohms. Its a lot more than needed. But the gains on the amp are set accordingly and the amp doesn't need to work nearly as hard to power the sub. My front speakers have a little more too. 110 watts rms x 2 @ 4ohms, and I'm running them with 125 watts rms x 2 @ 4 ohms. Hope that helps you out a bit.
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2011 Kona Blue MT82 V6 Mustang Pony Package 3:31 Gear Ratio, Interior Upgrade Pkg, Security & Shaker500/Sync
Mods (in order of installed): AM Bama SCT SF3 Tuner w/ 87 Hybrid Tune, Airaid CAI, Hurst Billet Plus 2 Short Throw Shifter, Lethal O/R H Pipe w/ Stock Exhaust, Blacked-Out Tints on Rear Windows, Full Ceramic Tint on Front Windows, Metra Touchscreen Dash Adaptor, Single DIN Head Unit, 6.5'' Component Speakers Fronts, Stock Rear Speakers, 10'' Sealed Subwoofer, 4ch. and 1ch Amplifier. LED licence plate lights, LED interior dome lights, FRPP/Dynamic shocks and struts, SR Performance lowering springs, GT500 Strut Mounts, BMR Adjustable Panhard Bar, BMR LCA's, BMR Relocation Brackets. Rear Seat Delete.