Try 400 trees and only 1 building (0 doesn't work, 1 will desactivate buildings).
Also, in the game settings, make sure you set your autogen density to the setting you need, depending on the visua result of the tweak. 400 and "Very Dense" will not look like 400 + "Sparse", see what I mean ? This has a strong impact on the performance.
For the FFTF, I have a Pentium 3,2 GHz, which is quite similar to your CPU, and I set it to 0.34.
For the TBM, start with 40 and see what happens. Then try 80 and compare.
The main tweaks do not exist by default in the FSX.cfg, you have to add them, in the correct section of course.
The bufferpools stuff, will have an impact on the performance while panning around, like when you're going forward, and suddently you decide to make a U-Turn, or to look around. The BufferPools will have an influence on the stutters you get whille turning. Try with 2500000, then eventually try with 5000000 (other members, please correct me if I'm wrong there, I'm not too sure about the number of zeros)
The settings in-game, as I mentionned before, should also be set in a appropriate maner. Here are my settings, and my hardware:
- Pentium 3,2 GHz
- 1 Gb RAM
- GeForce 6800 GT
Graphic settings:
- Ground texture 2m
- Scenery density "normal" (or even "sparse" sometimes, those scenery -not autogen- buildings are killing my video card)
- Autogen density at max (with max_trees at 800 and max_buildings at 800 as well
- Mesh resolution 19m
- Mesh complexity 100%
- Water... depends, sometimes Lox 2x, when I want some reflections on small lakes, sometimes High 1x, when I do not care
- FPS limit 17 (yes, it's low, but still smooth, and my scenery loads much faster !!)
Basically, I would say that the Scenery/Autogen density, the Ground Texture resolution and the FPS limit have the greatest impact on the performance. 1m textures look so cool, but I can't afford them with such a small CPU. I found the balance 2m/17 FPS to be quite pleasant for GA and gliding
Now you have to find what balance satisfies you best.