I have a SOHC 4.0, but I have had both the Delta 40 and Super 44. I liked the Delta pretty well, but it did not produce a lower sound like I wanted.
I currently have 2.5" piping from the cats back to a Super 44 (SI/DO) to 2.5" piping out the back at an angle under the bumper. This is by far my favorite setup I have ever had. I have had my truck for ~8 years and have had 6/7 different exhaust set ups on my truck.