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Those are their normal Street Series that only go for $895. The Pro Longtubes are $1800+. If I'm not mistaken the Pro's are bigger headers and built by borla. The street series are smaller, therefore less HP.
The link you provided shows the Pros going for $1595 and the Street series on sale for $895. It's my understanding that the street series uses a different style of merge collector - not as efficient/effective so you will lose a little power by comparison. The diameter of the pipes aft of the headers may also be smaller on the streets.
I think you forgot to add a 1 to that #, but thats ok. I've been told that you only loose like 5-10 Hp with the streets. I don't have them so I dont know for sure. Thats just what I've heard.
i have the LG SS, don't know what the difference as far as HP, but i know for sure that they leak on both ends of the cat converters using their supplied clamps.