I joined the forum to bring up the same complaint.
I 'upgraded' last week, from Win 7 HP sp1(different laptop) and from win 8 to 8.1 (this laptop via Windows Store).
Superfetch and indexing are not turned off. Accessing files in various devices seem to take forever compared to win 7.
Yesterday, I spent some time using the file explorer to rename and organize files on an external hard drive. Soon enough, the system came grinding to a slow crawl. Bringing up task manager took 'forever'. Eventually, it showed the explorer utilizing over 2GB of memory (6GB total in system). After closing the explorer window, the memory was not released. I had to restart explorer.exe to release the memory. Once I replicated the event, I began to wonder if this is unique to my machine or inherent in the OS.
I generally use XNView as my file manager. But, it wasn't performing as well as it should, or as well as it had been with Win 7. That's why I tried to bypass the middle man in XNView.
With Win 7, the external devices spin down after time has passed. There would always be lag while the accessed device spin up. With Win 8.1, the spin down seemed to be next to no time passing. I spend 5 to 10 seconds being careful in what I'm doing with the files, I have to deal with the lag before the action takes effect.
In summary, there is the explorer 'memory leak?' and the quick spin down of external devices, both affecting the performance of the file explorer.