I did the top pitch of Titan a few years ago on 8mm accessory cord, as I'd been reassured that it would be 'fine'. The rope's owner weighs about 60kg at most, whereas I'm more like 80kg. Needless to say 'fine' wasn't an apt description. My Stop became a Simple, and as my braking krab in those days was a normal steel oval, my descent was rather quicker than planned, accompanied by shrieking and swearing back up the pitch until they could no longer hear me. I managed to stop halfway down and wrap the rope around my leg and shoulder before squealing down to the Event Horizon in a rather sweaty state.
Climbing back up was not much improvement, as 8mm is more like 7mm when it's loaded, and my Croll was literally creaking under the strain of trying to grab this tiny, tiny rope.
That was probably the most nerve-wracking 15 minutes of my life, especially near the top. 😮