I searched and found a similar article. From what I can tell AGM and what I take away from it, is not ideal for DD cars. Gel Cell is still the best.
"AGM and other sealed batteries do not like heat and should be installed away from the engine compartment. Manufacturers recommend halting charge if the battery core reaches 49°C (120°F). "
That means trunk mount and even then, on a hot summer day a trunk in temperate climate could easily surpass that, in AZ, ambient temps could run that hot.
" Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell), and a direct replacement with a sealed unit could spell trouble by exposing the battery to undue overcharge on a long drive."
Again, not worth it. Go with a gel cell battery if you want better performance for your car unless it's a special application that is designed to handle an AGM battery.