We've know that most race pipes are rubbish for normal use and totally trounced by std pipes everywhere but at the top for a while now, wheather you can have your cake and eat it remains to be seen.
Maybe you can't, Keith's 74bhp monster made peak power before 11,000.
I'm seriously considering taking a Dremel to my OE '28 pipes and having them chromed, I'd be able to get at least the sort of mid range you're getting (the '28 dyno sheet is mine), run it on quiet trackdays and not get busted by the old bill.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread