I need to check whether or not the space inside this ducting is generous so I could pull thick cat7 and chunky plug through. I have no idea about the size, big is good.
To the best of my knowledge, the trunking to which I linked has a clip-on cover, so no need to pull the plugs through. As long as the cable fits, you just reattatch the cover. But do check that before ordering!
Echo other comments re adequacy of Cat 5e, or even just Cat 5. My home is wired with a mixture of cat 5 and 5e, generally carrying gigabit. Anytime I have checked re-tx stats on any of my ethernet devices, they have, with one exception, always been absolutely zero, even after weeks or months That exception was traced to hardware failure of a cheap Netgear switch, which manifested as data corruptions. Using Cat 7 (or even fibre) would not have fixed my broken switch, I’d still have got the corruptions. That said, Cat 7 will certainly do no harm.