I found a post on another forum that gives additional details if anybody's interested:
Hey All - I reached out directly to Borla re: difference between Borla S-type and Ford Performance Sport, and they responded quickly (thanks Borla). Based on this info, I'm going with Borla mid-section only (S or ATAK TBD). Below is what they told me:
"WE do make the Ford Racing systems for the Raptor and I would be glad to go over the differences between your options.
First, the Borla system is sold as two parts. The front x-pipe and muffler assembly are sold as one set and the tailpipes with our tips and new heat shielding are sold as a second set. The majority of our system is 2.75” but the pipes coming out of the muffler are 3” just so you can connect this to the stock 3” pipes or our tailpipes. The Ford Racing option is only available as a full Cat-Back and we decided to leave this as a full 2.75” system. It would be difficult to measure any difference in the performance and we have tuned the mufflers to take the respective sizes into account.
With regards to sound, the Ford racing system is noticeably quieter both at idle and under acceleration. If you can describe the type of sound you are looking for I should be able to point you in the right directly. I would also recommend taking a second look at the ATAK system, it is not much louder the our S-type system but it will provide a more aggressive tone that is higher pitch compared to the S-type which is a very low bass tone. All systems are guaranteed to be drone free.
If you choose to go with the Borla branded system you will see the vast majority of the sound improvement from the mid muffler section with only a small change from the tailpipes. The primary reason to purchase the tailpipes is for the heat shielding and the tips".