I don't know if this is helpful because my system is a bit different than yours (see sig):
I have had a lot of problems with game performance and also faced the issue that no matter which settings I used (low-med-high), the fps basically stayed the same.
After the November patches however, I did a clean re-install of the game and put everything on max. except shadows on the 2nd highest level. Now fps are constantly between 45-60fps. Even on Station, the fps drops are not happening anymore (1 exception).
I also used Tuneuputilities for register cleaning and all other options this programme is offering. I don't know if this helped in some way, but I just want to basically describe what changed my performance to almost double the fps.
Temperature of graca while playing HOS: about 70 degrees (celsius of course)
I am a noob when it comes to systems but some forum members helped me out and I am just stating my procedure. Maybe it is helpful for you or another person, who knows?!