Noticed a decrease in performance when higher detail scenery comes into play - with me, it seems the more detailed scenery in a view, such as airports or cities, my view rate goes down to around 9fps but haven't experienced your 6fps.   I experimented with the display/scenery setting etc and found I was best with the scenery options set to medium.   It seemed that switching-off dynamic scenery also helped & this setting seems distinct from the AI (artificial intelligence) aircraft in ATC, so it doesn't diminish the pleasure factor!  Good luck!   Dizzydave.