There probably isn't a single horsepower difference in the two. "Back in the day" , the Cobra intake was only 20-25 better than the stock iron four barrel intake. The Performer is about the same. now the Performer RPM or Air Gap is a bit better than the old Cobra. The Cobra has the WOW factor though. The modern Blue Thunder Cobra repop is very good too. I've run almost every 289-302 intake out there in my 50+ years of racing them. Power is limited by cylinder heads more than any other part.
'66 GT350H-3 time cover car - Car Craft July'77,Modified Mustangs and Fords Feb2011 ( w/article), Mustang Monthly June 2014. Bracket raced by me for the last 44 years. Yes it is a real one.
'68.5 R code GT fastback
'67 Ranchero 408W -427 glass hood
'78 F350 "Oleynik" car hauler
Ford Experimental parts collector