so you are going true duals correct?
Also you want really loud. Flowmaster Super 40's are pretty much same as the original 40's (slim to none difference) and spintechs are pretty much same as the original 40's. If I wanted loud i'd get 2 original 40 series and be done with. oh, btw, you're going to have a lot of drone.
since i'm not the the type that wants raspy or loud all the time I'd go with two dynomax super turbo mufflers. It's a straight through design like magnaflows and a lot quieter than chambered mufflers like flowmaster/spintech. Ever seen inside of a spintech muffler? not too impressive.
Soon I'm going with DHM Electronic Cutouts on my stock exhaust system. That'll be really LOUD.