I thought that the super 40's where louder than the original 40's but i could be wrong. I've had the delta flows and they have a little bit of tone but they were too quite for me. Personally I dont like flowmaster mufflers either way, they are behind the curve when it comes to acutally flow. Dynomax and Magnaflow are the two leading muffler companies when it comes to performance. I personally like Dynomax cause I'm not willing to pay an extra $60.00 just for it to say Magnaflow (that is littleraly what you are paying for).
As for an X pipe or an H pipe, they have acually done test and found that the H pipe slows the flow down and reduces flow through the exhuast, hindering performance, I dont have anyting wrong with a X pipe but at the same time i'm not a huge fan of them seeing as many people can listen to one side of the exhaust or the other and determine what is gong in inside that banks cylinders by the sound. You can't do that with a X pipe.