This question has appeared several times here in the past regarding weighing of carry-on.
We have just complected our 4th full trip, plus one with a transatlantic leg, on Lufthansa. That's a total of 17 flights, airports include Philadelphia, Frankfurt, Dusseldorf, Copenhagen, Amsterdam, Budapest, Newark, and a Munich transfer. In every case, we have appeared at the gate with our loaded RS convertibles on our backs. Not once were we ever requested to size or weigh these (they clearly fit the sizers). It is possible that the weight may have been a kilo over their 8 kg limit, it's hard to tell on our bathroom scale. We don't think they care since you are easily carrying it. For that matter, we have never been checked on other airlines, and that includes our first experience with Ryanair, which on this trip. That, BTW, was incredibly painless, especially as we bought our seats far-enough ahead with such a low price that the extra charge for priority was well worth it. We firmly believe if you show up with your pack on your back, without other hand-helds, you will not be checked. As if to prove that point, the only time one of our bags was rejected was on OrangeBus leaving Budapest several years ago. I had already boarded with my bag, but my wife was stopped because she was carrying her bag by hand to fit easily through the doors and struggling with it. She was thus made to place it under in the hold, with a surcharge, even though it was within their size limit and fit the overhead rack.