A similar experience for me too, Pete.
Around three or our years ago now and I was deadbaiting one October and I had taken three Pike to 22lb that morning, no problems at all with the gear.
It all went quiet until around 2.30pm when the float just slid away, none of the dips and slides that you typically get when a pike picks up the bait and the baitrunner slowly began clicking away.
At first I wondered if a large, submerged log had come down the river as I was just pulling a very heavy dead weight to the surface and when it broke the surface all hell broke loose, until that point I reckon it didn't even realise it was hooked but I clocked the mottled colouring as it went into an almighty S-shaped thrash and shot off UPRIVER at a pace that the drag on the reel couldn't keep up with and I ended up smashed to bits.
Hard to estimate a weight but I reckon it was a good five feet in length, if not more.
I remember looking into the gear needed to land one back at the time with a view to fishing a sleeper rod for them but even with strong enough gear I reckon I would have had to strap myself to a tree to be able to get enough winding power on it.
People do land 'em though so it can be done.