All things being equal, the same system will produce a higher SPL score in the Maxima. There's a lot more air in the Suburban, so the subs have to work a lot harder to move it. But, you can fit a lot more subs in the Suburban. It's kind of a catch 22. To hit huge SPL numbers, you need an SUV or a van due to the number of subs and amps you need to hit those numbers. But, for more practical systems, a smaller car will get you a higher SPL number.
id say the suburban //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif trunk cars are extremly hard to achieve high spl, a suburban may require low notes say 34-40hz due to the size of them but it has a lot more room like mentioned above to fit batts a large enclosure and amps where as my trunk space is pretty limited.