2. It is working very often when it seems it shouldn't - there is no I/O operations (or at least there shouldn't be any). For example during windows logon screen, before loging into windows.
3. When it encounter I/O operations it slowns down, and cause freezing the system/application.
It passes the SeaTool tests.
Although looking on HDTune you can see how low is minimum transfer.
Your burst and max rates are good, what does the health say?
I think you'll find the shabby min figure is due to interupts, you should turn off things like LAN and AV when testing, give that a try and see if things improve, but looking at what I see I don't think you have any worries tbh.
DOING ANYTHING I HAVE SUGGESTED IS AT YOUR OWN RISK, NEITHER I NOR SEAGATE TAKE ANY RESPONSIBILITY, IT'S YOUR CHOICE TO DO WHAT YOU FEEL IS BEST FOR YOU