A High power handling sub does not necessarily mean it's going to be loud. You also need to look at the sensitivity (dB or SPL[Sound pressure Level]) of the sub.
Sub "A" is 1000 watts RMS/85dB
Sub "B" is 500 watts RMS/95dB
Sub "B" would actually be louder than sub "A" because the sensitivity is higher even though the power handling of sub "A" is higher.
This is how that works:
The sensitivity of a sub is the SPL output the sub will have with 1 watt of power at 1 meter. For each doubling of power, you get a 3 dB gain in volume or SPL.
The left-most column is the power input to each sub. Each row is the expected dB output with the wattage provided. Each consecutive row is DOUBLE the power of the previous row.
Even at 1000 watts on Sub "A", Sub "B" still pushes more dB with only 500 watts.
NOTE: The examples above are calculated using an infinite baffle system in a free-air environment. Actual dB output will be higher and depend on many factors such as enclosure used, cabin gain, etc.