Brilliant information, thank you.
I have Easton EA50 clinchers on my Raleigh and they weigh in at 1785g a pair, plus around 325g for the Michelin Pro 4 tyres and whatever the tubes weigh. I have been looking at 24 or 38mm carbon rims to get a little more weight off, and was hoping to match or beat that with the new build.
I'll happily build the wheels myself, as I may well end up doing with the Raleigh, so I'll look at the rims you've mentioned, but I'll be looking for a low spoke count to keep weight down.
I do want a degree of durability, and having enjoyed a thorn (and the associated deflating feeling) from hedge cutting last autumn, that was my one reservation when it came to tubs.
I think I'll maybe look at a lightweight clincher build, with a careful choice of tubes and tyres.