Ben had a belting fish which I think was in the 7lb class a few years back which was one of the biggest I've seen 'real' evidence of in recent times.
I have seen older photos (1980s I'd guess) of fish that would have gone 9lb+ and bigger.
In the flesh I saw one that would have weighed a comfortable 7lb being returned somewhere on the Upper Don in the mid-'90s. No weigh net, no camera but it was a big, big fish and I still recall the size of the bow-wake it left as it stormed across the pool after being released. Unfortunately it was not to my rod and although I hunted that fish several times I never saw the bugger again
In my wanderings I've only ever seen a couple of fish that would have maybe gone double figures... none of them above Alford.
But, as we all know, these things are subjective.
H