That sounds exactly like my hard drive that failed without SMART errors. It really seems like your hard drive is failing. Just because it works better in Windows 8 or other systems, it does not mean that the HDD is OK. I experienced the exact same issue and it got worse and worse over time. Now my HDD only can read/write 1kb/s instead of several MB/s. So it technically “works”, but it is clearly failing.
Once I bought a replacement drive, cloned the contens from the old drive to the new one, everything was perfect again.
Do you have a replacement drive? If yes, try out if it is similarly slow. If it is not, your old HDD is most likely failing.