First off, it IS basic math. You were looking for the area of a circle = pi*radius*radius. Secondly, the 12s should be louder than the 10s since you have more surface area and more displacement of air. It might look "cooler" to have 4 woofers instead of 3, but it's purely a judgment call on your side. Either will work well and get unnecessarily loud in a muscle car. You should be focused on the engine not the stereo FYI.