The only tweak we recommend for all users is Highmemfix. This change to the fsx.cfg file allows FSX to better handle texture addressing modes when using high levels of video memory. It also helps a lot when memory is scares and for products like the Airbus X A320/A321 (formally known as the Airbus X Extended) it is almost obligatory. There are no negative effects reported. In our opinion, the Highmemfix line should be added to everyone’s fsx.cfg file.
Highmemfix must be added manually to the fsx.cfg file as shown below: