Wild brownies eh? I used to fish an overgrown stetch of the Goyt near Stockport. It was (and still is) free fishing and the brownies went to 4.5lbs. Great fish.
Recently, though, my local club acquired a length of the Bollin near Altrincham that hadn't been fished for a long time. A few big brownies started to come out so I thought I'd have a go. Result? A fish of 6.5lbs (yes - six and a half!). It was like a salmon. Other reports indicated fish up to just under 7lbs. I guess the message here is to look for little fished, neglected waters, as they may well contain monsters.
(PS: Also used to fish the Mersey near Stockport - again on free stretches that few anglers ever fished. Had bream to 4lbs and witnessed a fish of 8+lbs).