I have the highmem fix added, I have the sliders completely maxed out apart from air traffic I think (I have tried them with the default very high settings & have the same issues), here is a picture of the sort of things I get, which get worse the longer I play, within 10 minutes the game becomes completely unplayable.-
What are your system specs?
Yeah that is pretty typical situation when you max out all the sliders (particularly the scenery and water ones). Bring your water settings down to the x1 settings....the x2 water settings are absolute killers. Also ease back on the autogen density and bring the mesh settings back a bit too <- default FSX mesh is pretty poor so it doesn't really help having mesh set all the way up.
Also if you just want to have fun flying about in jet then I would consider completely disabling AI traffic as it has a large performance impact...apart from the AI traffic that you can see, FSX is also computing for up to dozens of AI aircraft in the area around you that you might not be aware of visually...it has to make sure they are all flying around properly and not crashing into one another
Disable light bloom from the FSX graphics menu too, this utterly destroys your frame rates, if you want light bloom effect the look up FSX ENB, the REX ENB's are pretty nice:
http://www.realenvironmentxtreme.com/forums/index.php?/topic/14771-natural-enbplus-download-included/
It gets worse the longer you play because the VAS is "filling up"...the more scenery you fly over and planes you load into the sim just keeps topping up the VAS usage and it doesn't go down...once FSX hits about the 3Gb mark of virtual space it will screw up one way or another.
I know this may seem odd as FSX in an older piece of software so a modern rig should be able to run it maxed out without breaking a sweat but it REALLY doesnt work like that with FSX; you could throw a NASA supercomputer at it and it would still run like a dog if you have all sliders maxed.
In modern games the computer is only asked to render what you are actually looking at on the screen...FSX doesnt work like this unfortunately....although you think you are just flying over your own town FSX is also thinking about rendering what is over the horizon, or around the other side of the world...it's a global simulation engine.
If you really want to get into FSX and you want to understand the performance issues with it then read this guide...it goes a long way to explaining how to get the best FSX experience from your system
http://kostasfsworld.wordpress.com/fsx-software-and-hardware-guide/
p.s. it's also worth noting that FSX does run better on nvidia cards...due to ATI basically abandoning FSX support at the driver level years ago, current AMD gpu's do not run FSX as well as geforce cards
If you want a one-stop-shop for a quick .cfg tweak then you can use this website, many people have much better performance after using the Ventubo automatic tweaker....just remember to backup your original FSX.cfg incase it goes t*ts up
http://www.venetubo.com/fsx.html