This is an interesting posting. I've had as much trouble as most getting good performance out of FSX, as turning off the autogen isn't really an option for me. Don't get me wrong, I'd never have a love-affair with autogen, but it did make one major difference to my sim when it was first introduced -- it put treelines on the hills when you are down low, or on the ground, and it broke up the landscape with a bit of 3D. Without these trees which sit between the hills and the sky it's pretty unrealistic, and turning it off in FSX would be like going back to the 90s.
Now I'd like more realistic autogen -- especially the Noddy-land buildings -- but it isn't as important as having autogen which doesn't bring the sim to its knees. Being able to see 12 different trees around my airports would be nice, compared to the current 3 or 4, but I have the feeling that this is something we might be able to use in FSXII.
To me, the autogen in FSX seems over-developed, and the effect on performance is greater than its contribution to the visual experience.
I find the performance of autogen very weird in FSX. Turning it up gives me no frame-rate hit for a minute or two, but then it gets slower and slower until I get a new frame every minute or so. At that stage all I can do is to Alt-F4 to shut it down. It'd be interesting to see if this would improve with more RAM headroom, or if it is similar to the pre-patch FS9's memory leak. I'd certainly like to hear from someone with a mid-specced machine but 2GB of RAM.
I'd try anything which reverts autogen to its FS9 performance level, but the other tweaks are less attractive. It does seem that it may be possible to get FSX working well eventually, I know I did it with FS9. It's just that it seems that a lot more work will be required this time around. And I'm not getting any younger.... mumble mumble...
