I've got a lot of 606 with significant weight on lath and plaster which is much worse than plasterboard. The fixings they provide are great and you're right about the number of fixings on the rail spreading the load. I have a problem with one area where there's a desk, extra leverage of course.
It's worse when you live and work in area that was all like that. A lot of it still was when I moved in 20 years ago. I have got better at dealing with it :)
I've got a lot of 606 with significant weight on lath and plaster which is much worse than plasterboard. The fixings they provide are great and you're right about the number of fixings on the rail spreading the load. I have a problem with one area where there's a desk, extra leverage of course.