I started with build 9860, and all was working well, until I had a problem with my hard drive after upgrade to 9879. I do not think this problem was caused by the system, but by me messing with my double drive (Raid 0) trying to separate them. The discs were fixed and I re-installed from an ISO, beginning as you did with build 9841, but I carried on to build 9860 and I waited for the slow update to build 9879 which I installed yesterday. So far so good. Even the change to OneDrive I am beginning to grasp.
I also liked Windows 8.1, although I think Windows 10 will be even better. I cannot talk in technical terms, just as a computer user. I find it all very interesting.
Paul - did you install Windows 10 on your main box or just on a test box?