There is actually only 1 Fatcat exhaust, there are 2 baffles for it........the standard baffle and the quiet baffle. The standard baffle has the louvered core with a solid outer can, while the quiet baffle has the louvered core with a perferated outer can with packing wrapped around it.
The other exhaust you are refering to is called the Borzilla, it is made for motors over 114". It has larger head pipes with a larger core to the baffle.....it flows a lot more air, but really only works on larger builds.
I just removed the standard baffle from my FatCat and replaced it with the quiet baffle, just to quiet it down a bit. There is a person on HDforum who did some testing for D&D comparing the 2 baffles on a dyno. His results were that the quiet baffle actually produces slightly better numbers while being just a bit quieter under acceleration and much quieter at idle and cruise.
Steve