One of the reasons they got the 323 HP was the fact the 3.6 is Direct Injection, it is good for a couple of more ponies but probably pretty close to be maxed out and able to meet EPA Standards.
As for the Shorties VS Long Tubes, I chose the legal for use on the public roads path with the Shorties, but there are a few of the Fastest 3.7's that switched to shorties from Long Tubes if that means anything.
2013 V6 MCoA, Performance Package, Security Package, Comfort Package and Electronic Package.
Mods OEM Backup Camera, BBK Shorties, FRPP Cut and Clamp X-Pipe, Borla Touring A/B's, Airaid CAI, Axle Xchange 2 piece aluminum Driveshaft, Koni Sport Shocks and Struts, Vogtland V6 Leveling springs, Ford Racing 302s wheels wrapped with Continental 275/40 19's, JBL GTO 8628 6X8 in all 4 corners. 2013 F 150 FX2 With a 6.2 Boss