I will say the AA Signature X-Pipe I installed replaced the primary cats with HFC's and replaced the secondary ones with resonators. I didn't notice any lag in any lower revs. I ran it for a week before I did the stage II tune. I hope that helps.
2009 AM V8 Vantage Conv - Berwick Bronze, Quicksilver Exhaust
2013 M3 Conv - (RIP) thanks to uninsured a-hole
2004 Porsche 911 C4S Conv