Brutus 1500bx and 2 800rms dvc @8 ohms

The current the amp pulls is dependent on the wattage of the amp.  1500 watts is power (P), 14 volts is voltage (E), and another factor is efficiency of the amp because some of the power is wasted in heat before it is changed to wattage for the subs.  A class D can be thought of as 85% efficient.  This is the formula:  I = (P / .85) / E with I being current.  This result in a current pull of 126 amps.  It may peak higher but I would believe 1500 is probably max output.  Or, you can use the amp's total fuses as your number for I.

In powering a load at 4 ohms, the amp will indeed produce much cleaner output and better quality.  The  RMS wattage is rated at 450.  Using the same formula, the amplifier would pull 38 amps at RMS power and will have peaks at times that will increase the pull.  There is much more headroom running the amp this way so you would figure power requirements on the peak pull...figure 60 - 65 amps.

The volume would be about 5 decibels greater if you used the amp at its 1-ohm 1500 watt output rating.  Stick with the cool 4 ohm load for better sound and make sure you have the proper enclosure for your subs.  It should be on the large side of the range.....what is the box you have at 1 cu. ft.?  This is for one sub?

Here is the spec link on the amp  http://www.maxxsonics.com/hifonics/ampsnew_brutus.html#

They also rated it @ 500 rms. So in essence my class a/b amp is around 60% efficient as opposed to the 85% of the class d so overall Id be getting more power vs my 2 channel bridged mode set up on my fosgate? Its rated rms pwr @ 14.4 is 710.

Well, I think you're talking about two different things.  Efficiency of an amp has only to do with how much power the amp pulls from the car. You asked earlier about how much the amp would draw.  Now you are comparing the amplifier's output power that tranlates into decibels.   When you compare two amps in terms of  "getting more power", you are comparing power output in watts.  I haven't researched the spec ratings of both these amps, but do your comparison with data that shows output at a common voltage input, such as both at 12 volts input. 

And, importantly, you will have to have a 4 ohm load (bridged) for the two channel amp to be equal in comparison to a 2 ohm load onto the mono amp.  Since you can wire your pair of subs to either 4 ohms or 1 ohm, your better choice for more power is to use the two channel amp bridged.  The 1 ohm load could only be put onto the mono amp and that is too much power for those subs. 

Keep in mind that the pull from your car's resources will be higher using the A/B amp.  For powering subs the efficiency of the class D will give you a better power-to-draw ratio, taking less resources for the same output.